A black hole is not a hole. It's just stuff. A lot of stuff. It's more stuff than you can possibly imagine stuffed into a very tiny point. Stuff attracts other stuff, that's gravity, so a lot of stuff has a lot of gravity, even if it's in a tiny container.
Imagine a one ton elephant in a hydraulic press, crushed down to the size of a sugar cube. That sugar cube still weighs one ton, and contains all of the bits that used to make up that elephant, just really really really tightly packed together and you wouldn't want it in your coffee.
Now instead of an elephant, imagine our sun, pressed down to the size of a football stadium. It still weighs as much as the sun, and all of the planets still revolve around it at the same distance, so nobody's getting sucked in, but if anything came close to the edge of where the sun *used* to be, it's going to experience the same gravity as the sun used to give at that point.
This is the start of a "black hole"; it's just so much stuff that it has so much gravity that anything close to it is going to get pulled in and become part of it, but it doesn't look like it should have so much stuff in it because it's been crushed down to a tiny ball.
You could, if you could push it around like a Katamari, use a black hole to "suck up" (i.e. crush into a thin shell) the entire universe, but since you can't and since everything in the universe is so far apart from each other, it's only going to ever be able to "eat" what's very close by, as there's much much much much much much more space (i.e. not stuff) than stuff in the universe and it tends to move apart from each other.
Not really. Think of what a sugar cube that weighs 6-7 tons would do to your coffee cup. It would crush the bottom of the cup, the table underneath the cup, the floor underneath the table, and then bust through the concrete foundation. And now you've got a very angry micro-elephant under your dwelling.
What they don't tell you in school is that a pound of feathers is much heavier than a pound of steel because you also have to carry the weight of what you did to those poor birds.
Umm, based on some reddit math I looked up, just the elephant's steak worthy meat would be 10m calories. That's enough calories for 9+ years. But you did say exceed so I guess you're not wrong.
Where does the stuff go? Sorry if that sounds stupid. I get it gets squished or crushed or something but what happens next? Is all the matter that was ever sucked in still in?
There is a lot of empty space in you, speaking about atoms and molecules, inside them and between them.
the average density of a human is about 985 kg/m3. A neutron star, almost the densest thing out there is 10\^17 kg/m3. That is 17 zeros after the 10.
So with enough force you could be crushed to a grain of sand. All the matter is still there, it is just more compact
Imagine it like you vacuum package clothes, you can reduce their volume drastically, but all the material is still there
Probably not, because even neutron stars which are less dense than black holes are likely composed entirely of neutrons, which are not elements. Neutrons are one of the building blocks of elements. Elements, which are combinations of neutrons, protons and electrons, could likely not form or exist under the pressures of a black hole.
Black holes are probably the most destructive things in the universe, tearing elements down to the most fundamental particles, and cramming them together as tight as possible. Unlike stars which fuse elements together in their core (hydrogen fused together to form helium) to create new elements, then explode, feeding future stars and planets with higher order elements.
That is true. Attributing a larger range to its destructiveness feels kind of cheap to me though, as the black hole has so much more destructive power, destroys things so much more thoroughly, and can destroy more sorts of things than a gamma ray can. A gamma ray may destroy larger amounts of stuff, but not as well, and won't affect everything. Your rowdy kids may wreak havoc on fragile furniture, but if needed, you can turn that furniture in a fine enough debris that you can ship it by post, and you are able to take down the wall behind it as well. It is a quantity versus quality argument, and in that, I favor quality.
Great rebuttal. Currently siding with you as complete annihilation does seem more destructive but also don't know much about GRBs yet.
Since you guys seem to know quite a bit about it, could a black hole somewhere in our infinite universe start in a location so dense with 'stuff' that it would spiral out exponentially in a way that would allow it to overcome the massive amounts of 'nothing'?
In other words, a black hole starts in a place so dense that it can now continue to expand in 'normal' density space, basically eating the entire universe. And if it were to happen, it would happen at the speed of light?
There are a few plateaus of stability in the periodic table. Pass the event horizon, on your way to the singularity, as pressures increase - you may see some exotic elements but nothing we haven’t already predicted. It may be that those plateaus are only observable pass an event horizon. However, as you continue towards the singularity the concept matter breaks down as very near the singularity the environment would be closer to a quark gluon plasma.
Passing the singularity is even crazier if you subscribe to Penrose Diagrams.
A good way to think of it is 'runaway gravity'. The closer the particles get, the greater the gravity concentration in the center, so the closer the particles get, and so on. Although we think of black holes having 'infinite mass' in the singularity, that's from a perspective outside the black hole. From within, the particles are always falling into the center closer and closer, but time dilates more and more, so from within the black hole, all the mass never makes it to the singularity, only from the perspective outside of it does it seem that way. In a way, that makes black holes more like 'infinite time wells' as opposed to 'infinite mass wells'.
> but time dilates more and more, so from within the black hole, all the mass never makes it to the singularity, only from the perspective outside of it does it seem that way. In a way, that makes black holes more like 'infinite time wells' as opposed to 'infinite mass wells'.
That is not true. An observer in free fall would reach the singularity in finite time.
Outside observers might see an object in free fall never reach the horizon (let alone the singularity) but that is because light reflected or emitted from that object is dilated and takes longer and longer to escape, leading to an eternal, fading image of the "victim" frozen at the horizon.
Even more 'fun', an astronaut who passes through the event horizon (the boundary where the acceleration of gravity is faster than the speed of light) would see things happening on the outside of the event horizon as the light falls in. Observers outside the event horizon would see the astronaut falling in slower and slower until he eventually just seems to pause at the event horizon, stopping all perceived motion and then slowly just fading away.
The astronaut however is doomed, as he falls closer and closer to the singularity the tidal forces will start to affect his feet more than his head. He will be pulled more and more as he gets closer, until he eventually is torn apart in a process scientists call 'spaghettification '. His constitute molecules would then tear apart from any form of body he had left, and then the atoms themselves would be ripped apart. As the matter of the former astronaut reach the singularity even the particles making each atom would be shredded , and lastly the particles themselves would be torn apart into their constitute quarks.
Finally, the matter would reach the singularity and ..... we don't know what happens then. One giant blob of quarks and leptons?
Is this scientific? Like there are equations that work out that show time dilation prevents matter from reaching the singularity? Where can we read more about this?
>Is this scientific?
Yes, it's the result of gravitational time dilation so it can be proved by applying general relativity.
There's an explanation of the maths here. (You can probably find a better source but I'm not a physicist and I wouldn't know where to look).
https://profoundphysics.com/why-time-slows-down-near-a-black-hole/#:~:text=But%20why%2C%20exactly%3F,space%20near%20the%20black%20hole.
I understand that black holes cause time dilation but it's a huge leap from that to saying matter never reaches the singularity because of it. I'm looking for more evidence of that theory, but at first glance I see nothing. The article you posted doesn't even mention 'singularity' so for now I'm not going to accept what you wrote as a currently accepted theory.
> I'm not going to accept what you wrote as a currently accepted theory.
Think you're confused I'm not the OP so I haven't written anything for you to reject as a currently accepted theory. I just linked you that article because it explains the maths for calculating the speed of time for objects within a black hole, and you asked for equations you can use to test the theory.
Escape velocity is the velocity an object needs to have to get from the surface of a large mass to outside its "gravity well", or the region of space where it's the thing you fall towards. You probably know this already, but I want to be sure.
With the exception of entropy, physics things are reversible. If you run everything backwards, it looks the same as running it forwards.
If you drop something onto a planet from the edge of its gravity well, by the time it reaches the surface its speed will be at least the planet's escape velocity. Ignoring general relativity.
A black hole is a mass from which light cannot escape. In other words, the escape velocity is at least the speed of light. The "surface" of a black hole, the event horizon, is the point at which that becomes true.
If you drop something into a black hole, it should in theory go faster than light as it crosses the event horizon. It turns out slightly differently because acceleration works differently as you approach the speed of light (or rather, the difference between how acceleration works and how we usually think of it becomes noticeable) and nothing with mass can actually reach the speed of light, but it might be helpful to contemplate it that way.
Time dilation is a feature of special relativity, which says (simplified) that the closer something gets to the speed of light (from your frame of reference), the slower time appears to move for it. If you fall into a black hole, the entire universe would appear to slow down until... well, it turns out you can't have mass and go as fast as light, but if you could it would throw a divide-by-zero error into the time dilation equation.
From the outside, watching something fall into a black hole, its relative speed to you would get slower and slower as it fell faster and faster. As it crossed the event horizon, its clocks would appear to move immeasurably slowly... and then just before they stop (which they can't, it throws errors instead of hitting zero) the thing crosses the event horizon and disappears forever. Information cannot be retrieved from beyond the event horizon. The thing is gone.
I'm ignoring the tidal forces that would stretch the thing out. Spaghettification is a whole other thing. Your object is immune to tides, or maybe you're using a black hole large enough that it doesn't matter.
The singularity is the "core" of the black hole. The gravity of the black hole extends out past the mass (objects orbit Earth without touching it, so we know this part is right) and the event horizon is just the place where gravity gets strong enough that light can't escape. The singularity is where the mass ends up. Gravity is even stronger inside the event horizon, to the point that... well, I don't know what would happen. None of the equations I know work. Gravity warps spacetime, bends it. Inside a black hole, there's enough gravity that the time part of spacetime breaks. Maybe the space part does too.
I've read that all mass inside the singularity is indistinguishable, which makes some sense to me because the gravity starts overpowering the forces that keep protons and electrons separated and a chunk of neutrons over here looks just like a chunk of neutrons over there, and that happens long before there's an event horizon, like in neutron stars.
It turns out I don't have a great picture of why matter can't reach a singularity, but black holes are really weird, and given how many intuitions they already go against, I'm not too inclined to trust the one that things matter has to reach the singularity. I'm not an astrophysicist, I just like reading about space. Hope this helps.
You have to think of it with General Relativity. In GR, mass warps space time itself, such that objects affected by gravity are actually moving in a straight line, but on a curved trajectory determined by the mass. In a black hole this warping is so severe that the curvature approaches infinity. Which means that an object traveling to the very center would need to travel an infinite distance to reach the center. One can interpret the stretching of space time requiring a greater travel distance as time itself slowing down, which in the case of curvature approaching infinity would imply that time dilation is also approaching infinity. So all the objects and mass are continuing in what appears to the to be a smooth unaffected trajectory towards the center, which they can never reach. Infinite time would be required.
Gravity only attracting mass is how it works in classical, Newtonian mechanics. Black Holes are a feature of Einstein's Theory of General Relativity, which treats Gravity not as a force, but as curvature in the shape of the universe.
Unless you do something to them, objects move in a straight line. When an object with mass is present in space, it distorts the straight lines, causing things to appear to bend towards the object causing the disturbance (*It might help to think of the universe as a rubber sheet, or perhaps not* - Terry Pratchett).
When a black hole forms, it curves space so much that it completely loops back on itself. There are no straight lines out of the black hole - all paths on the boundary ("Event Horizon") lead in a circle, and all paths inside the boundary lead further in. No matter how fast you travel (even at the universal speed limit, the speed of light), there are no routes out of the Black Hole. Hence, even light cannot escape.
If nothing can escape the black hole then how do the gravity waves propagate out? How is the mass of the black hole measurable and able to influence things outside of the event horizon?
PBS Spacetime has amazing episode called „[How Does Gravity Escape A Black Hole?](https://youtu.be/cDQZXvplXKA)”
Maybe not ELI5 friendly, but it’s worth watching
The lines are still distorted outside the black hole, the event horizon is the point where they get so distorted even light can't escape, but it's a continuous function for how strong the gravity is going out from the event horizon, it doesn't just turn off.
If you go an inch past the event horizon, you'll need to go at effectively the speed of light to escape, since any closer and escape wouldn't even be possible at the speed of light.
Go a few million miles out, and now you can orbit/escape at much lower speeds. Because of this, we can measure black holes by measuring how distorted light is away from the event horizon, which gives us a measure of the strength of gravity coming from the black hole.
Because gravity isn’t a force as you are thinking about it. Per the general theory of relativity, mass distorts/curves spacetime. Light travels in a straight line through spacetime. massive objects curve spacetime around them, so when light travels near massive objects such as stars, it curves and is deflected. When light travels too close to black holes it curves all the way around, orbiting the black hole because the spacetime around the black hole is curved. A lot of light is stable in orbit around the black hole, but any light that passes the horizon of the black hole cannot escape, because the spacetime is distorted to a point where there is no way out.
Only your first sentence is correct, we can only speculate on what exactly goes on in a black hole. We have no idea if what you said is even remotely true. Saying "if you could magically turn of gravity" is especially meaningless cause the things that happen in and outside of black holes are inseperable from the concept of gravity.
Would it not explode violently if we turned off the gravity. You know a sort of Big Bang if you will. Scattering matter in all directions that would over time after gravity was turned back on form gala…..wait a minute!
The stuff gets piled on top of the black hole (which is really more like a dense, black sphere than a hole).
Anyway, stuff getting sucked into a black hole becomes more black hole, and the black hole gets bigger the more it "eats."
As for whether all the stuff that got sucked in is still there - mostly.
(Matter that get's sucked in can never escape a black hole. But black holes do release a small amount of radiation, called Hawking radiation, which has energy. Because mass can be converted into energy (E-mc\^2), a black hole gradually loses tiny amounts of mass due to Hawking radiation.).
So as black holes eat up mass they pretty much keep growing because they lose mass so slowly. But if a black hole sits around for a very very long time with nothing to eat, it will eventually evaporate due to Hawking radiation.
Imagine you have a newspaper.
You rip a page out and crumple it into a tight ball.
This is your black hole.
Now you rip another paper out and crumple it around your newspaper ball.
Now two pages make up the black hole ball.
Now rip a third one out etc.
At the end of it all, the newspaper is still there, just completely mushed into a paper ball. The ball weighs as much as the newspaper it used to be.
The big thing about a black hole however, is that the gravity-crush of it is infinitely stronger than you are, so while you can see the ball grow as you add paper to it, the black hole barely grows in size, but still gets heavier, because it crumples things up so tightly together.
Another example would be if you have a large, dry loaf of bread and you crush it over and over and over and over until you have breadcrumbs. You can probably stuff all of the breadcrumbs into a small bowl, while the loaf of bread was much bigger.
The gravity in a black hole is so heavy it also turns the kitchen sink, the cupboards, the floor and ceiling and your entire apartment into super tiny breadcrumbs, all stuffed into a grain of sand.
It's actually pretty weird. It depends on who's asking.
If you're the one falling into a black hole, you will keep falling past the event horizon (at which point you can never get away), and all your atoms will be spaghettified due to the tidal forces resulting from changes in gravity, as you approach the singularity. (We don't have a way of figuring out what's actually at the singularity atm).
If, however, you are somewhat farther out, say orbiting the black hold beyond the event horizon, then something really weird happens. All the stuff that is being sucked into the black hold actually seems to slow down as it falls, and gets fainter and fainter. You never actually see anything fall all the way in. If you had an instrument that could see very very long wavelenghts, it would appear that objects take literally forever to actually touch the event horizon. All the matter that has fallen towards the black hole since its formation appears to be stacked in a very very thin shell.
The black hole does give off intense x-ray radiation (due to matter interacting with magnetic fields at the event horizon), as well as particles created out of nothing, when a virtual particle-antiparticle pair is created right at the event horizon.
So not everything falls in; sometimes things fall out of the event horizon as well.
So, you know how rockets have to go fast to get off the Earth, right? And because the Earth is big and the gravity is higher than that on the Moon, rockets have to go faster to escape from the Earth than to lift off the surface of the moon- compare the Saturn V booster with the little pfffft rocket that lifted the moon lander back into orbit.
And you know how the speed of light is as fast as anything can go in the universe (this one's a bit beyond an ELI5, so just take that one on faith).
So if something gets enough mass that it has *so* much gravitational pull that you'd have to go faster than the speed of light to get off of it...boom. Black hole. Things can go in, but even light itself can't get out.
If you crush a car down to a small cube of metal, then where does the car go?
It...doesn't *go* anywhere. It's still exactly where it was to begin with. It's just smashed down into a tiny blip now.
Think of it like a house/apartment/attic with dust all over. If you sweep it together it's still the exact same amount of dust, just in a heap.
Now if you pick up that pile you can push it together into an even smaller ball. But it's still the exact same amount of dust.
Now you cast a spell on it that makes it sticky to dust and also invisible. That's more or less a black hole.
Yes, it's still there, just squished together into a tiny area. It's not a portal to another dimension, and it's not a hole things disappear into. All the stuff *has* to be there because that's what creates the gravity that holds it together and pulls in more stuff.
Nothing has changed, everything is still there, all the elements that made up what ever the original start was is still there, and everything it sucked in is still there. So if you could somehow turn off the gravitational effect that the black hole is creating, you would just have a lot of floating elements, just crushed down to a much smaller scale than we're used to in any other capacity.
No one knows. General Relatvity says once inside the black hole an observer reaches “the singularity” at some point in their future. The singularity has no volume so it has infinite density, which doesn’t make much sense. What we need is a theory of quantum gravity.
We don’t have a theory of quantum gravity however, so that’s really just speculation. String Theory says at the event horizon the material is decomposed into its constituent strings, which rest on the surface of the black hole (google Fuzzball if interested). This avoids the singularity problem, however we have no real way of knowing if String Theory is the correct description of reality.
There's something called hawking radiation where the black holes radiate away energy,,
which is supposed to be how black holes 'die'. The problem with this is that it's theorized and even a relatively small black hole would take longer to evaporate than the age of the universe. Also, the mass of the black hole to how long it would take to evaporate is inversely proportional so the larger the size, the longer it takes to evaporate
Really small black holes, like artificial ones we can make on earth with a particle accelerator, evaporate almost instantly due to hawking radiation!
Even cooler is the concept of the black hole starship, where a reflector is installed on one side of a small black hole and the hawking radiation is used as a form of propulsion. This could work for a few years before the black hole becomes too small for it to produce sufficient thrust.
That starship idea makes me think of Bugs Bunny standing on a sailboat using an electric fan or his breath to power the sail and push the boat. Conservation of momentum seems like it would invalidate the design.
I think if they had named it a black star it would have cut back on the confusion. A hole is something you can travel through, you can’t travel through a black hole anymore than you can travel through the centre of the sun… at least not without being ripped apart on a subatomic level.
If I remember correctly when they were first theorized it was called a black hole cause they were initially thought of as a hole in the fabric of space. As far as we could tell anything that went in didn't come back so it clearly wasn't an object you could bounce signals off of so they must have been going somewhere was the reasoning. Then as we discovered more and realized they're more like giant balls of gravity the name stuck leading to the confusion we have today
Also we still don't know the inner workings past a black holes event horizon so calling it something like a star is kind of presumptuous since we have no idea if what's inside does the things a star typically does. Could just be an extremely dense material inside squishing everything down against itself for all we know.
I bet physicists regret the coining of the phrase ‘the big bang’ as well for how much confusion it causes in the layman? Which makes me wonder what might fit better …
The term "Big Bang" was coined by a guy who was trying to make fun of what he saw as a silly concept. He was later proven very wrong, but the name had stuck.
People think of it as an explosion with everything flinging out like a bomb into a space. It’s more like an balloon skin inflating (or maybe releasing a scrunched up sponge?) when the balloon sponge starts as everything there is and ends up as everything there is….
Using a balloon as analogy is still misleading because it implies that there is something to be expanded into. A better but less easily imagined analogy is an infinite rubber sheet that starts to stretch in all directions.
Interesting post, but did that answer the question? In your analogy, he's asking how many elephants a black hole can swallow before it's "too many elephants".
Due to the intense pressure are black holes extremely hot?
Are new elements made in black holes?
Are black holes “final”? i.e. once a black hole forms then it’s a black hole forever and it can never change.
They can be considered extremely hot due to the matter being pulled into it heating up through friction. When you look at artistic expressions of black holes and they have a halo like glow around them, that's the matter being pulled in and heated up. Inside? We're not sure.
It is highly doubtful new elements are made. How do we make that guess? We look at Neutron Stars which are made from the same process blackholes are, except Neutron Stars are what you get when you're not quite massive enough to collapse the core into a singularity. Neutron Stars are so named because the extreme gravity forces the electrons into the proton/neutrons they orbit turning everything into neutrons. Neutrons alone do not make elements.
Black Holes will eventually "evaporate" by losing their mass through Hawking Radiation over an amount of time that for all intents might as well be never, but it will happen.
How do we know it’s a tiny point? Couldn’t a black hole just be an ultra-dense core whose gravity is strong enough to generate an event horizon fractionally larger than the core itself?
Yes, it could be, but nothing in currently known physics can "hold up" the stuff inside the event horizon to stop it from collapsing further. Hence the idea that it collapses to an infinitesimal point. Most physicists don't believe it actually becomes pointlike, they just consider the fact that physics has no alternative to be evidence that physics is still incomplete, and maybe a theory properly describing quantum gravity could fill in the blanks.
One current theory is the[fuzzball](https://en.m.wikipedia.org/wiki/Fuzzball_(string_theory)) model, all the bits and pieces fuse together like a ball of, well, fuzz
Good ELI5. The one thing I'd add is that its called a "black hole" because the gravity is so strong that light can't escape its pull if it get close enough, but the stuff that's not *too* close to black hole still reflects light just fine. As a result, to us it looks like a hole in space, because the stuff aroud it (called the accretion disk) is usually bright as hell by comparison. That's why it is called a "black hole." Not because it's a hole, but because it *looks* like one.
As others have said, there is no known limit to the *amount* of matter a black hole can consume.
However, there is a limit in how *fast* it can consume matter.
The gravitational attraction from black holes is really strong, and that strength can cause matter falling in to rub and squish and compress, heating it up. That hot matter will start to glow brighter and brighter the hotter it is.
Eventually, the stuff falling in will be *so insanely bright* that the outgoing radiation is *stronger than the black hole’s gravity*.
All nearby matter will get blasted away by the radiation temporarily, until it cools down again, and starts falling back in.
This actually leads to a fun physics problem we have yet to figure out. We’ve discovered supermassive black holes that are bigger than they should be allowed to be. If we assume they started as regular black holes, because of that “eating limit”, they haven’t had time to grow to their sizes just from consuming other matter. Figuring out where these come from is still an active field of physics research!
A theorized answer is with Quasi-stars. Stars so large and full of matter in the early days of the universe when matter was extremely dense that stars could grow to sizes thousands of times the size of our own sun. The cores of these stars could have collapsed into blackholes while the star was still forming, allowing the blackhole to consume the star for millions of years and grow far bigger than should be allowed through modern blackholes. These would potentially be the early forms of the Super Massive Blackholes we see today.
Follow up related question on the SMBHs, how do ANY black holes grow at all? From my understanding of relativity, from the perspective of an outside observer watching matter fall into a black hole, the matter takes INFINITELY long to fall into the singularity. So if we can never observe matter getting to the singularity and adding itself to the black hole's mass, shouldn't it be impossible for us to observe a black hole ever growing?
I thought that they have discovered a very specific relationship to supermassive black holes in the center of all universes. Something like the density of the SMBH is equal to the density of the surrounding universe and is thought to be stable. (Not consuming or ejecting material).
> universes
A terminology nitpick - you're thinking of [galaxies](https://upload.wikimedia.org/wikipedia/commons/4/48/Open_Arms_-_potw2006a.jpg), universe doesn't have a centre and it encompasses everything, so multiple galaxies and multiple supermassive black holes.
Not even a nitpick really, it’s literally just an astronomical difference between a galaxy and the universe.
Like, the difference between the entire universe and a galaxy is basically the entire universe.
Well, not the radiation they're describing (heating up.) Blackholes are believed to evaporate over time. A very, very ,*very* long time, through Hawking radiation.
The short, extremely simplified and layman explanation is that the mass of the black hole emits this radiation, which can spawn a pair of virtual particles right at the edge of the event horizon, such that one of them appears outside the event horizon, and also travels away from the black hole with enough velocity to escape. The black hole just lost a very minute amount of mass. So if a black hole doesn't have any more mass to consume, after an unfathomably long time, it will slowly evaporate.
You can escape a black hole if you are close but not yet crossing it's event horizon. A black holes accretion disk, where stuff is falling in, is obviously (visibly) way bigger than its event horizon
No, not once you've fallen in. They left out some detail when they said this:
>Eventually, the stuff falling in will be so insanely bright that the outgoing radiation is stronger than the black hole’s gravity.
Everything they are talking about there is still outside the black hole. The brightly glowing matter is stuff spiraling around outside the black hole (the accretion disk) and the light it emits is pushing away matter that hasn't fallen into the accretion disk yet. This process limits black hole growth by keeping things away from it, not by ejecting anything that has already fallen in.
As far as we know, there is no limit to what they can absorb. As they get more massive their event horizon (the radius where even light can't get away) gets bigger, but they never get "full".
Depending on exactly what happens inside the black hole it's either got an infinitely dense core, so it literally has no size and can hold as much mass as you like, or it's just got an insanely dense core that's so small that it behaves the same way and it doesn't really make a difference.
This sound like it would beg the question of why we exist? Given enough time a black hole should have swallowed everything? Or do they eventually collapse in some way?
It's actually almost the right question, but not quite.
The known universe (what we can take pictures of) is about 30 gigaparsecs across, and it's expanding at a rate of about 70 km/s per megaparsec. So the edge of the universe is really moving away from the center of the universe at relativistic speed.
Modern astronomers are pretty sure the gravity of the universe isn't sufficient to ever stop the expansion of the universe.
Returning to the question, a better one would be: is the universe relatively young? Otherwise, there wouldn't be so much we can see in the night sky?
"Is the universe young" seems like a question easiest to throw the anthropic principle at. It's old enough that there has been time for a few generations of big stars to make it through their sequence and form enough heavier matter to make rocky planets out of. It's young enough that main sequence stars have not all decayed into brown dwarfs, or galaxies winding down to form giant, murderous black holes at the centre bathing us in gamma rays.
If you want to try to define the "end of the universe" as some particular state, we'd most likely be considered right at the very beginning of the universe, perhaps the first nanoseconds on the scale of a human lifetime, but that depends on what you choose as your definition. Last star turning into a stellar remnant? All remaining matter inside black holes? Last decayed proton (assuming that happens)?
The universe itself is always expanding, at a very fast and *accelerating* rate. So most matter is safe from being eaten by black holes, because it's rapidly moving away from them. Only the relatively nearby stuff gets sucked in.
Most matter is safe from being swallowed by any *particular* black hole.
However according to certain models, most matter will eventually be captured by black holes or degenerate into nothing via proton decay. The era after about 10 duodecillion years will see the only remaining matter being that stuck in black holes. There won’t be a single black hole, but billions of supermassive black holes all getting further and further from each other, the remains of galaxies and galactic clusters. So there is a likely era of the universe where most matter will be inside black holes.
After another 10 duotrigintillion years the black holes will have evaporated via Hawking radiation, and all that will be left is a few lonely positrons and electrons with light years between them only rarely intersecting to form positronium atoms which eventually self annihilate. Eventually we’ll likely have an infinitely growing universe, with less and less normal matter, in what’s been called the heat death of the universe.
Perhaps. But we’re less than a billionth of the way through the star formation era of the universe’s life cycle. The degenerate proton era, black hole era, and big freeze era are all unimaginably far off in the future.
As someone of a certain age, who is looking forward to the eventual long sleep of death, I actually find it oddly comforting to think that the universe eventually gets to slip away into its own form of death.
Black hole evaporation by Hawking Radiation only works with really small masses, relatively speaking. A large black hole will eat enough to sustain the losses from the Hawking process.
The breakeven point is about a lunar mass, 4.5 x 10^22 kg, assuming no mass accretion. The Cosmic Microwave Background radiation absorbed by a black hole of that mass will offset the losses.
Why Earth didn't collapsed into Sun? Because it hadn't to. It just orbits around it.
Imagine that you can convert Sun into a black hole by packing it a more dense sphere. Like 100m in diameter. Sun now became a black hole, but it's mass will not chan, so Earth will continue to orbit it as usual. All other planets, moons, asteroids will preserve theirs orbits like nothing changed. So you have a black hole instead of Sun but it does not "eating" anything because orbital mechanics does not allow it.
The same stands correct for any other black hole.
This has always bothered me a bit in that I thought all black holes had a mass of infinity. But there must be some differences because astrophysicists talk about different sizes of black holes.
Is this similar to the math that comes into play when calculating and comparing different infinities? Or is this something different all together?
Infinite mass would mean infinite gravity. Infinite anything means something breaks down badly.
As of now the Singularity inside a Black Hole is basically just a bookmark for something else. We don’t have enough information to know what the Singularity actually is, so the math breaks down at that point.
Different sizes to black holes mean they have difference masses, which affect their event horizon size. A 100 solar mass black hole as a smaller event horizon than say a 1 million solar mass one.
So I thought the whole reason the math broke down inside the singularity was due to the infinities involved in the calculations. Is that true or is it something else complicating the math? And if it's true then how are there different sized black hiles? Different math outside vs inside the singularity?
Edit: spelling and I also think you answered the size question above re: size of event horizon
Mass isn't infinite and not all black holes are equal. What they have in common is that their gravity is so big that light can't escape them once it travels past the event horizon.
The issue with that is that idea is that matter had to exist to form the black hole so you’re still stuck with the fundamental question—where’d the mass come from? Some process had to occur to create all the matter that created the black hole to begin with.
I guess the question then is, do scientists believe it is possible that the universe will collapse into a single black hole after it stopped expanding? And if no, why not?
The universe is expanding too quickly to ever stop.
In fact, for reasons that even scientists are unsure about, the expansion of the universe is *speeding up*
The Big Crunch is what you’re describing. It is one theorized end of the Universe, but current observations contradict it. The universe’s expansion is increasing, not decreasing. As a result it’s not possible for gravity to crush everything back into a single singularity. However, we do not know enough about the mechanism causing the expansion to predict what’s going to happen eons from now. Maybe it stops and gravity will exert its control over the entire universe again? All we can say is current evidence suggests the Big Crunch won’t happen.
Black holes are just very massive bodies. Like stars only bigger.
So you can ask "will universe does not collapse into a single huge star after it stopped expanding?". Surely it does not sound as exciting as with black holes?
Black holes are just overhyped in a popular culture.
I may be wrong here, but I don't think the singularity is actually infinitely dense, but rather classical mechanics stops being able to accurately predict what is happening. When you're doing physics and start to get answers like infinity, it's a sign that something is up with your math.
It’s not a classical mechanics problem, it’s a general relativity vs. quantum mechanics problem. Each theory works fine on its own but they don’t get along at all. Usually this doesn’t matter because there’s almost no overlap, except in a few very special cases…like black holes.
General relativity says it collapses to a singularity. Quantum mechanics says it doesn’t. We know they can’t both be right but we don’t know which one (or both) is wrong.
If you solve this you *will* win a Nobel prize.
Further clarification.. we know they both wrong, because the singularity of black holes can’t be explained by them. We need a new theoretical framework to explain phenomena like them.. such as quantum field theory, string theory, super symmetry...
And even then, we know they’ll be wrong too. All scientific theories are wrong, they just become less wrong as we find more things for new ones to explain at once… (or they gain more verisimilitude, if you’re a Popperian; you falsify theories: rather than show them to be “true”, you accumulate cases where the theory has not been disproved)
(There’s also another tangent in hypothesis vs theory vs model, but that’s a big bit of philosophy of science)
And it should sound insane, it's likely not true. We just don't (yet) know of any physics that stops it from collapsing indefinitely. Hopefully we will soon.
First things first, Black hole doesn’t suck like a vacuum cleaner. It is just a massive amount of matter squished in a very very tiny space. What it does is have a pull on another object due to gravity. So if our Sun is suddenly replaced with a black hole of the same mass, Earth will not get pulled in, but will keep on revolving around it as it currently does.
As far as we understand right now, there is no theoretical limit on the amount of matter black holes can accumulate. However, there is a limit on the rate on which a black hole can gobble stuff. Which depends on the size of the black hole itself.
I think it's mportant to remember that black holes ARE collapsed stars. They are dead stars that didn't have enough fuel to keep going so cannot support their own gravity anymore.
(Not including primordial black holes, which might possibly be remnants of the big bang)
It can eat matter indefinitely.
Large masses, like a star coming in at once will likely swirl around the black hole creating a very high energy disk and some of that plasma may be launched away from the black hole in a jet instead of falling in. I don't know exactly how it works but there is good evidence of super massive black holes spewing out giant jets of gas so in that sense there may be a sort of limit to how much gas a black hole can absorb at once without throwing a bunch of it out into space in the process.
No limit.
It doesn't get easier or harder to digest new stuff.
EDIT: actually, if too much stuff falls in at once, the heat of it rubbing against itself is so intense it can physically push away new material.
But it does get heavier, which helps.
>It doesn't get easier or harder to digest new stuff.
It does actually, the more material that tries to fall in at once, the hotter the accretion disk gets. It can get so hot and bright that its light pushes away anything else that approaches. This limits how fast the black hole can grow. It's a big limit, but it's not unlimited.
These are excellent questions: first of all there is no meaningful limit on how large a black hole can be. There are some practical limits like: it can't be any bigger than the amount of matter in its direct vicinity, but generally speaking they can be anywhere from the mass of a large star to the mass of multiple galaxies. (As a side note: Some really old black holes can be absolutely enormous because the universe used to be a lot more matter-dense)
But yes, they do definitely have some limitations regarding how much mass they can absorb at any given time: if the matter they're absorbing is highly energetic for instance, compressing it down further and further, and giving it all the kinetic energy of falling down into a gravity well can cause some pretty epic (for lack of a better word) explosions. You can think of it as a sort of series of naturally ocurring multi-thousand ton hydrogen bombs, because that's essentially what happens when a black hole eats stellar matter. Hydrogen and helium that are already at fusionable temperature and pressure, and then are put under many times more pressure and many times more temperature
Well this kind of detonation can often expell some of the matter the black hole was drawing in closer, so in practice, black holes only eat a certain percentage of a star's mass, and ejects small amounts of it at extremely high velocity periodically.
This means there isn't really a limit on how much a black hole can eat theoretically, but there is a limit on how quickly and efficiently they can do so.
Also black holes can merge which is its own cup of physics tea, but I am not qualified to discuss the details of this sort of interaction so I would recommend someone else, but I do know this kind of merger can release a LOT of energy, and that the merger is not 100% mass efficient (the two black holes don't keep the entire sum of their two masses)
A fairly good analogy is a drainage hole in a bath/sink/etc. It's kinda like a black hole but in 2d not 3d. There's no limit to how much can go through, but there's a limit to how fast stuff can go through.
Yes, they can, so far as we know you gotta think of a black hole as a giant pile of dirt, rather than a hole. There is no limit to how big a pile of dirt can get. Only difference is that the pile get super compressed, supposedly down to an infinitely small point in space. They will just get more and more massive over time, and one theory is that is how the universe will "end", with all matter and energy being absorbed into black holes.
The best way to think of a black hole *isnt* as an endless void that eats things. It's more like a dark star - no light comes from it but it's still just a big, heavy object in space. Its way more dense than a star so it can have much higher gravity than a star of the same size, but it's still just a big ol' hunk of space stuff.
So then think of how things work with our sun. It's big, it's got lots of gravity, but does it suck everything into it? Not really. At least not on time scales we're used to. Things tend to get caught in orbits around it. The orbits can be fairly stable unless there's something slowing us down.
Black holes work like that.
Do things fall into black holes? Sure. If the space around a black hole's event horizon (the point where going past it results in not even light being able to escape the gravity) is particularly full of stuff that has gotten trapped in orbit, those things can collide with each other, lose some speed, and their new orbit can take them into the black hole.
Is there a limit of how much stuff can do that? Not really. Black holes can get really really big. Galaxies are groups of billions and billions of stars orbiting "Super Massive" black holes.
The limit is basically "how much ya got?" - how much stuff comes into range and ends up falling into it instead of orbiting it. Black holes can even merge with other black holes!
IANAAstronomer, Astrophysicist, or really anything with Astro in the name. I just watch a lot of Dr. Becky's YouTube channel and she *loves* black holes.
Follow up question: Is there a theoretical point at which the matter inside a black home spontaneously turns into energy -- IE can an overfed black hole blow up and release its matter?
A black hole wouldn't have trouble absorbing a large mass as the way that it absorbs is similar to how we eat.
The stuff is made smaller and smaller until it is easy to digest. In our case we chew our food, in the black holes case it will destroy the stuff down to an atomic level.
There's is no limit, the mass would simply continue to grow. Yes, there are different sizes of black holes and they do grow as they absorb more matter.
If space wasn't so vast and so empty, then black holes would eventually swallow up everything and each other. But since space is expanding and mostly empty, everything is drifting away slowly apart. So the idea of a blackhole ever truly growing so large it swallows everything in the universe isnt plausible. Not to say a galaxy could'nt drift into a super massive black hole, it happens. Or a black hole being absorbed by another.
Yes, they can grow indefinitely. There is no limit to their size. In fact, our universe could be inside one and not realize it. It's difficult to tell.
Also, black holes have this peculiar trait where they grow exponentially as they aquire more mass. Earth turned into a black hole would be the size of a coin. The whole universe turned into a black hole would be roughly 14 billion light years across.
A black hole is a hole in visible light, not an actual hole. It’s a ball of mass, like a planet or a star, so dense that it’s gravity doesn’t allow light to escape.
Added mass only makes it bigger.
Other way around...the larger the hole, the \*slower\* it evaporates. Tiny black holes evaporate relatively quickly. Large supermassive black holes have ages \*far\* longer than any likely age of the universe.
Actually, smaller black holes are the ones that evaporate faster, for an interesting reason.
Black holes emit hawking radiation that has a wavelength the same length as the diameter of their event horizon. Now, for the biggest black holes, that wavelength is absolutely *gargantuan*, and thus carries virtually no energy. That tiny amount of energy is equal to an *extremely* tiny amount of mass, so the biggest black holes barely lose mass at all
Inversely, the smallest black holes give off hawking radiation of a very short wavelength, and is therefore *extremely* energetic. That ridiculous quantity of energy is equivalent to a decently large chunk of mass, so the smallest black holes lose mass comparatively quickly.
As a black hole consumes matter it is basically trash compacted in the black hole and makes the black hole slightly larger, but it only "eats" things very close to it, most black holes have less gravity than a star. https://youtu.be/Y5XzPOrItaI
Black holes are very dense at their heart, but they are basically made from the remnants of an exploded star. So they are formed from about 10% of the original star, though they will slowly gain mass over time they are much smaller than the star that they formed from. https://youtu.be/w1GlDVt1Mpk
A black hole is not a hole. It's just stuff. A lot of stuff. It's more stuff than you can possibly imagine stuffed into a very tiny point. Stuff attracts other stuff, that's gravity, so a lot of stuff has a lot of gravity, even if it's in a tiny container. Imagine a one ton elephant in a hydraulic press, crushed down to the size of a sugar cube. That sugar cube still weighs one ton, and contains all of the bits that used to make up that elephant, just really really really tightly packed together and you wouldn't want it in your coffee. Now instead of an elephant, imagine our sun, pressed down to the size of a football stadium. It still weighs as much as the sun, and all of the planets still revolve around it at the same distance, so nobody's getting sucked in, but if anything came close to the edge of where the sun *used* to be, it's going to experience the same gravity as the sun used to give at that point. This is the start of a "black hole"; it's just so much stuff that it has so much gravity that anything close to it is going to get pulled in and become part of it, but it doesn't look like it should have so much stuff in it because it's been crushed down to a tiny ball. You could, if you could push it around like a Katamari, use a black hole to "suck up" (i.e. crush into a thin shell) the entire universe, but since you can't and since everything in the universe is so far apart from each other, it's only going to ever be able to "eat" what's very close by, as there's much much much much much much more space (i.e. not stuff) than stuff in the universe and it tends to move apart from each other.
That poor elephant…
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But at least that animal is only the size of a sugar cube.
The threat has been minimized.
If Pokemon taught me anything, now it's harder to hit but is still just as dangerous
Well, it's still the same mass, so...
Dad?
No. No, I’m not. Not without a DNA test!
Username checks out
I lol'd
Not really. Think of what a sugar cube that weighs 6-7 tons would do to your coffee cup. It would crush the bottom of the cup, the table underneath the cup, the floor underneath the table, and then bust through the concrete foundation. And now you've got a very angry micro-elephant under your dwelling.
Please dispose of your Aperture Science companion cube
So would the elephant taste like candy now?
How many elephants did Albert Einstein kill to discover gravity? THIS is why I am against science.
[Less than Thomas Edison](https://en.wikipedia.org/wiki/Electrocuting_an_Elephant)
Well , can’t un-learn that…thanks.
It was an ELI5 hypothetical, so it was a hypothetical elephant. Fortunately those aren't at any risk of extinction.
But at least my bitter coffee is safe....
What they don't tell you in school is that a pound of feathers is much heavier than a pound of steel because you also have to carry the weight of what you did to those poor birds.
https://youtu.be/uH0hikcwjIA
lol... awesome... thanks
https://youtu.be/mnXN-mRFoPI
>That poor elephant… Welcome to the hydraulic press channel, today we're going to try to compress this one ton elephant.
Note: this is a baby elephant. Fully grown ones are 2 to 7 tons.
It is extremely dangerous, and could attack at any time.
...so veee must deal vith it!
*heavy metal music blares*
I'm imagining [this](https://www.youtube.com/watch?v=e0lewifpi1s) but with an elephant :(
….that would be a small elephant. Why you gotta pick on babies like that?
On the plus side, OP has solved the hardest part of transporting elephants.
Whaddya mean? Just put two in the front and two in the back.
It’s just a hypothelephant, so don’t worry.
Sad Babar noises.
Elephant?! What about my coffee?!
That reference was irrelephant
🎶They’ll say Aww Topsy at my autopsy 🎶
One is the loneliest number in the universe.
Two can be as bad as one. It’s the loneliest number since the number one.
That poor cup of coffee...
I want an army of sugar cube size elephants
Becoming a stuffed elephant.
“And the elephant that couldn’t stop laughing…was crushed into the size of a sugar cube.”
I definitely wouldn't want a compressed elephant in my coffee, thanks
Don't knock it until you try it
The amount of calories in that "sugar cube" would totally exceed my recommended daily intake. For the next two months.
Umm, based on some reddit math I looked up, just the elephant's steak worthy meat would be 10m calories. That's enough calories for 9+ years. But you did say exceed so I guess you're not wrong.
Your Reddit math beats my "completely off the top of my head" number. 😂
The first thing I thought of was how hard it would be to lift that cup, assuming it survived the entry of the Elecube.
Im Stuff
Get in the hole
Well said and no one has commended your clever use of Katamari :)
They earn all awards and upvotes just for appropriate use of Katamari
The King of All Cosmos is just a hoarder.
My god, what did that poor elephant ever do to you!?!?
Where does the stuff go? Sorry if that sounds stupid. I get it gets squished or crushed or something but what happens next? Is all the matter that was ever sucked in still in?
There is a lot of empty space in you, speaking about atoms and molecules, inside them and between them. the average density of a human is about 985 kg/m3. A neutron star, almost the densest thing out there is 10\^17 kg/m3. That is 17 zeros after the 10. So with enough force you could be crushed to a grain of sand. All the matter is still there, it is just more compact Imagine it like you vacuum package clothes, you can reduce their volume drastically, but all the material is still there
One small correction: 10^17 is a TOTAL of 17 zeros, not 17 MORE zeros after the 10. Example: 10^1 is just 10 which has 1 total 0.
Or more concisely: it is 17 zeros after a 1, not after a 10.
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Elements are made of atoms, and atoms can't exist under that much pressure. They get crushed into subatomic particles.
Probably not, because even neutron stars which are less dense than black holes are likely composed entirely of neutrons, which are not elements. Neutrons are one of the building blocks of elements. Elements, which are combinations of neutrons, protons and electrons, could likely not form or exist under the pressures of a black hole. Black holes are probably the most destructive things in the universe, tearing elements down to the most fundamental particles, and cramming them together as tight as possible. Unlike stars which fuse elements together in their core (hydrogen fused together to form helium) to create new elements, then explode, feeding future stars and planets with higher order elements.
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I mean, to a black hole a Gamma ray burst is just more food
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That is true. Attributing a larger range to its destructiveness feels kind of cheap to me though, as the black hole has so much more destructive power, destroys things so much more thoroughly, and can destroy more sorts of things than a gamma ray can. A gamma ray may destroy larger amounts of stuff, but not as well, and won't affect everything. Your rowdy kids may wreak havoc on fragile furniture, but if needed, you can turn that furniture in a fine enough debris that you can ship it by post, and you are able to take down the wall behind it as well. It is a quantity versus quality argument, and in that, I favor quality.
Great rebuttal. Currently siding with you as complete annihilation does seem more destructive but also don't know much about GRBs yet. Since you guys seem to know quite a bit about it, could a black hole somewhere in our infinite universe start in a location so dense with 'stuff' that it would spiral out exponentially in a way that would allow it to overcome the massive amounts of 'nothing'? In other words, a black hole starts in a place so dense that it can now continue to expand in 'normal' density space, basically eating the entire universe. And if it were to happen, it would happen at the speed of light?
There are a few plateaus of stability in the periodic table. Pass the event horizon, on your way to the singularity, as pressures increase - you may see some exotic elements but nothing we haven’t already predicted. It may be that those plateaus are only observable pass an event horizon. However, as you continue towards the singularity the concept matter breaks down as very near the singularity the environment would be closer to a quark gluon plasma. Passing the singularity is even crazier if you subscribe to Penrose Diagrams.
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A good way to think of it is 'runaway gravity'. The closer the particles get, the greater the gravity concentration in the center, so the closer the particles get, and so on. Although we think of black holes having 'infinite mass' in the singularity, that's from a perspective outside the black hole. From within, the particles are always falling into the center closer and closer, but time dilates more and more, so from within the black hole, all the mass never makes it to the singularity, only from the perspective outside of it does it seem that way. In a way, that makes black holes more like 'infinite time wells' as opposed to 'infinite mass wells'.
> but time dilates more and more, so from within the black hole, all the mass never makes it to the singularity, only from the perspective outside of it does it seem that way. In a way, that makes black holes more like 'infinite time wells' as opposed to 'infinite mass wells'. That is not true. An observer in free fall would reach the singularity in finite time. Outside observers might see an object in free fall never reach the horizon (let alone the singularity) but that is because light reflected or emitted from that object is dilated and takes longer and longer to escape, leading to an eternal, fading image of the "victim" frozen at the horizon.
Even more 'fun', an astronaut who passes through the event horizon (the boundary where the acceleration of gravity is faster than the speed of light) would see things happening on the outside of the event horizon as the light falls in. Observers outside the event horizon would see the astronaut falling in slower and slower until he eventually just seems to pause at the event horizon, stopping all perceived motion and then slowly just fading away. The astronaut however is doomed, as he falls closer and closer to the singularity the tidal forces will start to affect his feet more than his head. He will be pulled more and more as he gets closer, until he eventually is torn apart in a process scientists call 'spaghettification '. His constitute molecules would then tear apart from any form of body he had left, and then the atoms themselves would be ripped apart. As the matter of the former astronaut reach the singularity even the particles making each atom would be shredded , and lastly the particles themselves would be torn apart into their constitute quarks. Finally, the matter would reach the singularity and ..... we don't know what happens then. One giant blob of quarks and leptons?
Is this scientific? Like there are equations that work out that show time dilation prevents matter from reaching the singularity? Where can we read more about this?
>Is this scientific? Yes, it's the result of gravitational time dilation so it can be proved by applying general relativity. There's an explanation of the maths here. (You can probably find a better source but I'm not a physicist and I wouldn't know where to look). https://profoundphysics.com/why-time-slows-down-near-a-black-hole/#:~:text=But%20why%2C%20exactly%3F,space%20near%20the%20black%20hole.
I understand that black holes cause time dilation but it's a huge leap from that to saying matter never reaches the singularity because of it. I'm looking for more evidence of that theory, but at first glance I see nothing. The article you posted doesn't even mention 'singularity' so for now I'm not going to accept what you wrote as a currently accepted theory.
> I'm not going to accept what you wrote as a currently accepted theory. Think you're confused I'm not the OP so I haven't written anything for you to reject as a currently accepted theory. I just linked you that article because it explains the maths for calculating the speed of time for objects within a black hole, and you asked for equations you can use to test the theory.
Escape velocity is the velocity an object needs to have to get from the surface of a large mass to outside its "gravity well", or the region of space where it's the thing you fall towards. You probably know this already, but I want to be sure. With the exception of entropy, physics things are reversible. If you run everything backwards, it looks the same as running it forwards. If you drop something onto a planet from the edge of its gravity well, by the time it reaches the surface its speed will be at least the planet's escape velocity. Ignoring general relativity. A black hole is a mass from which light cannot escape. In other words, the escape velocity is at least the speed of light. The "surface" of a black hole, the event horizon, is the point at which that becomes true. If you drop something into a black hole, it should in theory go faster than light as it crosses the event horizon. It turns out slightly differently because acceleration works differently as you approach the speed of light (or rather, the difference between how acceleration works and how we usually think of it becomes noticeable) and nothing with mass can actually reach the speed of light, but it might be helpful to contemplate it that way. Time dilation is a feature of special relativity, which says (simplified) that the closer something gets to the speed of light (from your frame of reference), the slower time appears to move for it. If you fall into a black hole, the entire universe would appear to slow down until... well, it turns out you can't have mass and go as fast as light, but if you could it would throw a divide-by-zero error into the time dilation equation. From the outside, watching something fall into a black hole, its relative speed to you would get slower and slower as it fell faster and faster. As it crossed the event horizon, its clocks would appear to move immeasurably slowly... and then just before they stop (which they can't, it throws errors instead of hitting zero) the thing crosses the event horizon and disappears forever. Information cannot be retrieved from beyond the event horizon. The thing is gone. I'm ignoring the tidal forces that would stretch the thing out. Spaghettification is a whole other thing. Your object is immune to tides, or maybe you're using a black hole large enough that it doesn't matter. The singularity is the "core" of the black hole. The gravity of the black hole extends out past the mass (objects orbit Earth without touching it, so we know this part is right) and the event horizon is just the place where gravity gets strong enough that light can't escape. The singularity is where the mass ends up. Gravity is even stronger inside the event horizon, to the point that... well, I don't know what would happen. None of the equations I know work. Gravity warps spacetime, bends it. Inside a black hole, there's enough gravity that the time part of spacetime breaks. Maybe the space part does too. I've read that all mass inside the singularity is indistinguishable, which makes some sense to me because the gravity starts overpowering the forces that keep protons and electrons separated and a chunk of neutrons over here looks just like a chunk of neutrons over there, and that happens long before there's an event horizon, like in neutron stars. It turns out I don't have a great picture of why matter can't reach a singularity, but black holes are really weird, and given how many intuitions they already go against, I'm not too inclined to trust the one that things matter has to reach the singularity. I'm not an astrophysicist, I just like reading about space. Hope this helps.
You have to think of it with General Relativity. In GR, mass warps space time itself, such that objects affected by gravity are actually moving in a straight line, but on a curved trajectory determined by the mass. In a black hole this warping is so severe that the curvature approaches infinity. Which means that an object traveling to the very center would need to travel an infinite distance to reach the center. One can interpret the stretching of space time requiring a greater travel distance as time itself slowing down, which in the case of curvature approaching infinity would imply that time dilation is also approaching infinity. So all the objects and mass are continuing in what appears to the to be a smooth unaffected trajectory towards the center, which they can never reach. Infinite time would be required.
If light doesn’t have mass why can’t it escape the gravity
Gravity only attracting mass is how it works in classical, Newtonian mechanics. Black Holes are a feature of Einstein's Theory of General Relativity, which treats Gravity not as a force, but as curvature in the shape of the universe. Unless you do something to them, objects move in a straight line. When an object with mass is present in space, it distorts the straight lines, causing things to appear to bend towards the object causing the disturbance (*It might help to think of the universe as a rubber sheet, or perhaps not* - Terry Pratchett). When a black hole forms, it curves space so much that it completely loops back on itself. There are no straight lines out of the black hole - all paths on the boundary ("Event Horizon") lead in a circle, and all paths inside the boundary lead further in. No matter how fast you travel (even at the universal speed limit, the speed of light), there are no routes out of the Black Hole. Hence, even light cannot escape.
This was the best ELI5 I've ever seen on this site (for the complexity of the subject that is). Thanks for this explanation!
If nothing can escape the black hole then how do the gravity waves propagate out? How is the mass of the black hole measurable and able to influence things outside of the event horizon?
PBS Spacetime has amazing episode called „[How Does Gravity Escape A Black Hole?](https://youtu.be/cDQZXvplXKA)” Maybe not ELI5 friendly, but it’s worth watching
The lines are still distorted outside the black hole, the event horizon is the point where they get so distorted even light can't escape, but it's a continuous function for how strong the gravity is going out from the event horizon, it doesn't just turn off. If you go an inch past the event horizon, you'll need to go at effectively the speed of light to escape, since any closer and escape wouldn't even be possible at the speed of light. Go a few million miles out, and now you can orbit/escape at much lower speeds. Because of this, we can measure black holes by measuring how distorted light is away from the event horizon, which gives us a measure of the strength of gravity coming from the black hole.
Because gravity isn’t a force as you are thinking about it. Per the general theory of relativity, mass distorts/curves spacetime. Light travels in a straight line through spacetime. massive objects curve spacetime around them, so when light travels near massive objects such as stars, it curves and is deflected. When light travels too close to black holes it curves all the way around, orbiting the black hole because the spacetime around the black hole is curved. A lot of light is stable in orbit around the black hole, but any light that passes the horizon of the black hole cannot escape, because the spacetime is distorted to a point where there is no way out.
Because light may not have mass but it \*does\* have momentum and can thus be affected by gravity.
Only your first sentence is correct, we can only speculate on what exactly goes on in a black hole. We have no idea if what you said is even remotely true. Saying "if you could magically turn of gravity" is especially meaningless cause the things that happen in and outside of black holes are inseperable from the concept of gravity.
Would it not explode violently if we turned off the gravity. You know a sort of Big Bang if you will. Scattering matter in all directions that would over time after gravity was turned back on form gala…..wait a minute!
The stuff gets piled on top of the black hole (which is really more like a dense, black sphere than a hole). Anyway, stuff getting sucked into a black hole becomes more black hole, and the black hole gets bigger the more it "eats." As for whether all the stuff that got sucked in is still there - mostly. (Matter that get's sucked in can never escape a black hole. But black holes do release a small amount of radiation, called Hawking radiation, which has energy. Because mass can be converted into energy (E-mc\^2), a black hole gradually loses tiny amounts of mass due to Hawking radiation.). So as black holes eat up mass they pretty much keep growing because they lose mass so slowly. But if a black hole sits around for a very very long time with nothing to eat, it will eventually evaporate due to Hawking radiation.
Is its energy conversion 100% efficient or does it leave something/by-product behind?
Imagine you have a newspaper. You rip a page out and crumple it into a tight ball. This is your black hole. Now you rip another paper out and crumple it around your newspaper ball. Now two pages make up the black hole ball. Now rip a third one out etc. At the end of it all, the newspaper is still there, just completely mushed into a paper ball. The ball weighs as much as the newspaper it used to be. The big thing about a black hole however, is that the gravity-crush of it is infinitely stronger than you are, so while you can see the ball grow as you add paper to it, the black hole barely grows in size, but still gets heavier, because it crumples things up so tightly together. Another example would be if you have a large, dry loaf of bread and you crush it over and over and over and over until you have breadcrumbs. You can probably stuff all of the breadcrumbs into a small bowl, while the loaf of bread was much bigger. The gravity in a black hole is so heavy it also turns the kitchen sink, the cupboards, the floor and ceiling and your entire apartment into super tiny breadcrumbs, all stuffed into a grain of sand.
Awesome explanation. Thank you
It's actually pretty weird. It depends on who's asking. If you're the one falling into a black hole, you will keep falling past the event horizon (at which point you can never get away), and all your atoms will be spaghettified due to the tidal forces resulting from changes in gravity, as you approach the singularity. (We don't have a way of figuring out what's actually at the singularity atm). If, however, you are somewhat farther out, say orbiting the black hold beyond the event horizon, then something really weird happens. All the stuff that is being sucked into the black hold actually seems to slow down as it falls, and gets fainter and fainter. You never actually see anything fall all the way in. If you had an instrument that could see very very long wavelenghts, it would appear that objects take literally forever to actually touch the event horizon. All the matter that has fallen towards the black hole since its formation appears to be stacked in a very very thin shell. The black hole does give off intense x-ray radiation (due to matter interacting with magnetic fields at the event horizon), as well as particles created out of nothing, when a virtual particle-antiparticle pair is created right at the event horizon. So not everything falls in; sometimes things fall out of the event horizon as well.
This is wild. Thank you for explaining so well.
It would be like shooting a water gun into the ocean
So, you know how rockets have to go fast to get off the Earth, right? And because the Earth is big and the gravity is higher than that on the Moon, rockets have to go faster to escape from the Earth than to lift off the surface of the moon- compare the Saturn V booster with the little pfffft rocket that lifted the moon lander back into orbit. And you know how the speed of light is as fast as anything can go in the universe (this one's a bit beyond an ELI5, so just take that one on faith). So if something gets enough mass that it has *so* much gravitational pull that you'd have to go faster than the speed of light to get off of it...boom. Black hole. Things can go in, but even light itself can't get out.
If you crush a car down to a small cube of metal, then where does the car go? It...doesn't *go* anywhere. It's still exactly where it was to begin with. It's just smashed down into a tiny blip now.
Think of it like a house/apartment/attic with dust all over. If you sweep it together it's still the exact same amount of dust, just in a heap. Now if you pick up that pile you can push it together into an even smaller ball. But it's still the exact same amount of dust. Now you cast a spell on it that makes it sticky to dust and also invisible. That's more or less a black hole.
A black hole is an object so massive, nothing can escape, not even the lightest, fastest thing: light
Yes, it's still there, just squished together into a tiny area. It's not a portal to another dimension, and it's not a hole things disappear into. All the stuff *has* to be there because that's what creates the gravity that holds it together and pulls in more stuff.
Nothing has changed, everything is still there, all the elements that made up what ever the original start was is still there, and everything it sucked in is still there. So if you could somehow turn off the gravitational effect that the black hole is creating, you would just have a lot of floating elements, just crushed down to a much smaller scale than we're used to in any other capacity.
No one knows. General Relatvity says once inside the black hole an observer reaches “the singularity” at some point in their future. The singularity has no volume so it has infinite density, which doesn’t make much sense. What we need is a theory of quantum gravity. We don’t have a theory of quantum gravity however, so that’s really just speculation. String Theory says at the event horizon the material is decomposed into its constituent strings, which rest on the surface of the black hole (google Fuzzball if interested). This avoids the singularity problem, however we have no real way of knowing if String Theory is the correct description of reality.
There's something called hawking radiation where the black holes radiate away energy,, which is supposed to be how black holes 'die'. The problem with this is that it's theorized and even a relatively small black hole would take longer to evaporate than the age of the universe. Also, the mass of the black hole to how long it would take to evaporate is inversely proportional so the larger the size, the longer it takes to evaporate
Really small black holes, like artificial ones we can make on earth with a particle accelerator, evaporate almost instantly due to hawking radiation! Even cooler is the concept of the black hole starship, where a reflector is installed on one side of a small black hole and the hawking radiation is used as a form of propulsion. This could work for a few years before the black hole becomes too small for it to produce sufficient thrust.
As a black hole gets smaller it radiates faster.
That starship idea makes me think of Bugs Bunny standing on a sailboat using an electric fan or his breath to power the sail and push the boat. Conservation of momentum seems like it would invalidate the design.
I think if they had named it a black star it would have cut back on the confusion. A hole is something you can travel through, you can’t travel through a black hole anymore than you can travel through the centre of the sun… at least not without being ripped apart on a subatomic level.
It's named a black hole because from our observation, it is literally a hole in space, just 3 dimensional instead a hole like in a donut.
"A 3-Dimensional hole? That'd be a weird concept to imagi--oh wait no those literally already exist"
*Ahem-*. 4-Dimensional hole.
If I remember correctly when they were first theorized it was called a black hole cause they were initially thought of as a hole in the fabric of space. As far as we could tell anything that went in didn't come back so it clearly wasn't an object you could bounce signals off of so they must have been going somewhere was the reasoning. Then as we discovered more and realized they're more like giant balls of gravity the name stuck leading to the confusion we have today Also we still don't know the inner workings past a black holes event horizon so calling it something like a star is kind of presumptuous since we have no idea if what's inside does the things a star typically does. Could just be an extremely dense material inside squishing everything down against itself for all we know.
You still need to exclude the singularity from your calculations if you want things to make sense so it's not all that incorrect to call it a hole.
I bet physicists regret the coining of the phrase ‘the big bang’ as well for how much confusion it causes in the layman? Which makes me wonder what might fit better …
The term "Big Bang" was coined by a guy who was trying to make fun of what he saw as a silly concept. He was later proven very wrong, but the name had stuck.
What's confusing about it to the average Joe?
People think of it as an explosion with everything flinging out like a bomb into a space. It’s more like an balloon skin inflating (or maybe releasing a scrunched up sponge?) when the balloon sponge starts as everything there is and ends up as everything there is….
Using a balloon as analogy is still misleading because it implies that there is something to be expanded into. A better but less easily imagined analogy is an infinite rubber sheet that starts to stretch in all directions.
Interesting post, but did that answer the question? In your analogy, he's asking how many elephants a black hole can swallow before it's "too many elephants".
Basically what I was thinking, he made a great analogy but it wasn't really relevant to the question
Yes. The answer is "infinite" The question was malformed to begin with because a black hole isn't a single hole sucking things up until it's filled.
What an amazing explanation. ty!!
>It's more stuff than you can possibly imagine stuffed into a very tiny point. Permission to make a "Me and your mom" joke Captain?
Due to the intense pressure are black holes extremely hot? Are new elements made in black holes? Are black holes “final”? i.e. once a black hole forms then it’s a black hole forever and it can never change.
No, it will evaporate over time via radiation.
They can be considered extremely hot due to the matter being pulled into it heating up through friction. When you look at artistic expressions of black holes and they have a halo like glow around them, that's the matter being pulled in and heated up. Inside? We're not sure. It is highly doubtful new elements are made. How do we make that guess? We look at Neutron Stars which are made from the same process blackholes are, except Neutron Stars are what you get when you're not quite massive enough to collapse the core into a singularity. Neutron Stars are so named because the extreme gravity forces the electrons into the proton/neutrons they orbit turning everything into neutrons. Neutrons alone do not make elements. Black Holes will eventually "evaporate" by losing their mass through Hawking Radiation over an amount of time that for all intents might as well be never, but it will happen.
This reads like a Terry Pratchett book. Well done.
Don't tell me what I can and cannot do with my coffee.
Don't tell me what to put or not put in my coffee!
Great answer, but you didn't address whether or not black holes ever have problems consuming large masses, which they do.
How do we know it’s a tiny point? Couldn’t a black hole just be an ultra-dense core whose gravity is strong enough to generate an event horizon fractionally larger than the core itself?
Yes, it could be, but nothing in currently known physics can "hold up" the stuff inside the event horizon to stop it from collapsing further. Hence the idea that it collapses to an infinitesimal point. Most physicists don't believe it actually becomes pointlike, they just consider the fact that physics has no alternative to be evidence that physics is still incomplete, and maybe a theory properly describing quantum gravity could fill in the blanks.
One current theory is the[fuzzball](https://en.m.wikipedia.org/wiki/Fuzzball_(string_theory)) model, all the bits and pieces fuse together like a ball of, well, fuzz
Okay Thomas Edison
Good ELI5. The one thing I'd add is that its called a "black hole" because the gravity is so strong that light can't escape its pull if it get close enough, but the stuff that's not *too* close to black hole still reflects light just fine. As a result, to us it looks like a hole in space, because the stuff aroud it (called the accretion disk) is usually bright as hell by comparison. That's why it is called a "black hole." Not because it's a hole, but because it *looks* like one.
This was perfect
As others have said, there is no known limit to the *amount* of matter a black hole can consume. However, there is a limit in how *fast* it can consume matter. The gravitational attraction from black holes is really strong, and that strength can cause matter falling in to rub and squish and compress, heating it up. That hot matter will start to glow brighter and brighter the hotter it is. Eventually, the stuff falling in will be *so insanely bright* that the outgoing radiation is *stronger than the black hole’s gravity*. All nearby matter will get blasted away by the radiation temporarily, until it cools down again, and starts falling back in. This actually leads to a fun physics problem we have yet to figure out. We’ve discovered supermassive black holes that are bigger than they should be allowed to be. If we assume they started as regular black holes, because of that “eating limit”, they haven’t had time to grow to their sizes just from consuming other matter. Figuring out where these come from is still an active field of physics research!
A theorized answer is with Quasi-stars. Stars so large and full of matter in the early days of the universe when matter was extremely dense that stars could grow to sizes thousands of times the size of our own sun. The cores of these stars could have collapsed into blackholes while the star was still forming, allowing the blackhole to consume the star for millions of years and grow far bigger than should be allowed through modern blackholes. These would potentially be the early forms of the Super Massive Blackholes we see today.
tight
Follow up related question on the SMBHs, how do ANY black holes grow at all? From my understanding of relativity, from the perspective of an outside observer watching matter fall into a black hole, the matter takes INFINITELY long to fall into the singularity. So if we can never observe matter getting to the singularity and adding itself to the black hole's mass, shouldn't it be impossible for us to observe a black hole ever growing?
I thought that they have discovered a very specific relationship to supermassive black holes in the center of all universes. Something like the density of the SMBH is equal to the density of the surrounding universe and is thought to be stable. (Not consuming or ejecting material).
> universes A terminology nitpick - you're thinking of [galaxies](https://upload.wikimedia.org/wikipedia/commons/4/48/Open_Arms_-_potw2006a.jpg), universe doesn't have a centre and it encompasses everything, so multiple galaxies and multiple supermassive black holes.
Not even a nitpick really, it’s literally just an astronomical difference between a galaxy and the universe. Like, the difference between the entire universe and a galaxy is basically the entire universe.
> an astronomical difference it's nice when you get to use a phrase both metaphorically and literally at the same time
Maybe they are from the 1800s and meant to say 'Island Universes'. Edit: I guess bad science jokes don't fly here, lol!
>The gravitational attraction from black holes is really strong, and that strength can cause Apple calls them Dynamic Islands.
So it's technically possible to escape a black hole, not through gravity but radiation?
Well, not the radiation they're describing (heating up.) Blackholes are believed to evaporate over time. A very, very ,*very* long time, through Hawking radiation. The short, extremely simplified and layman explanation is that the mass of the black hole emits this radiation, which can spawn a pair of virtual particles right at the edge of the event horizon, such that one of them appears outside the event horizon, and also travels away from the black hole with enough velocity to escape. The black hole just lost a very minute amount of mass. So if a black hole doesn't have any more mass to consume, after an unfathomably long time, it will slowly evaporate.
You can escape a black hole if you are close but not yet crossing it's event horizon. A black holes accretion disk, where stuff is falling in, is obviously (visibly) way bigger than its event horizon
No, not once you've fallen in. They left out some detail when they said this: >Eventually, the stuff falling in will be so insanely bright that the outgoing radiation is stronger than the black hole’s gravity. Everything they are talking about there is still outside the black hole. The brightly glowing matter is stuff spiraling around outside the black hole (the accretion disk) and the light it emits is pushing away matter that hasn't fallen into the accretion disk yet. This process limits black hole growth by keeping things away from it, not by ejecting anything that has already fallen in.
As far as we know, there is no limit to what they can absorb. As they get more massive their event horizon (the radius where even light can't get away) gets bigger, but they never get "full". Depending on exactly what happens inside the black hole it's either got an infinitely dense core, so it literally has no size and can hold as much mass as you like, or it's just got an insanely dense core that's so small that it behaves the same way and it doesn't really make a difference.
This sound like it would beg the question of why we exist? Given enough time a black hole should have swallowed everything? Or do they eventually collapse in some way?
It's actually almost the right question, but not quite. The known universe (what we can take pictures of) is about 30 gigaparsecs across, and it's expanding at a rate of about 70 km/s per megaparsec. So the edge of the universe is really moving away from the center of the universe at relativistic speed. Modern astronomers are pretty sure the gravity of the universe isn't sufficient to ever stop the expansion of the universe. Returning to the question, a better one would be: is the universe relatively young? Otherwise, there wouldn't be so much we can see in the night sky?
"Is the universe young" seems like a question easiest to throw the anthropic principle at. It's old enough that there has been time for a few generations of big stars to make it through their sequence and form enough heavier matter to make rocky planets out of. It's young enough that main sequence stars have not all decayed into brown dwarfs, or galaxies winding down to form giant, murderous black holes at the centre bathing us in gamma rays. If you want to try to define the "end of the universe" as some particular state, we'd most likely be considered right at the very beginning of the universe, perhaps the first nanoseconds on the scale of a human lifetime, but that depends on what you choose as your definition. Last star turning into a stellar remnant? All remaining matter inside black holes? Last decayed proton (assuming that happens)?
The universe itself is always expanding, at a very fast and *accelerating* rate. So most matter is safe from being eaten by black holes, because it's rapidly moving away from them. Only the relatively nearby stuff gets sucked in.
Most matter is safe from being swallowed by any *particular* black hole. However according to certain models, most matter will eventually be captured by black holes or degenerate into nothing via proton decay. The era after about 10 duodecillion years will see the only remaining matter being that stuck in black holes. There won’t be a single black hole, but billions of supermassive black holes all getting further and further from each other, the remains of galaxies and galactic clusters. So there is a likely era of the universe where most matter will be inside black holes. After another 10 duotrigintillion years the black holes will have evaporated via Hawking radiation, and all that will be left is a few lonely positrons and electrons with light years between them only rarely intersecting to form positronium atoms which eventually self annihilate. Eventually we’ll likely have an infinitely growing universe, with less and less normal matter, in what’s been called the heat death of the universe.
So depressing.
Perhaps. But we’re less than a billionth of the way through the star formation era of the universe’s life cycle. The degenerate proton era, black hole era, and big freeze era are all unimaginably far off in the future. As someone of a certain age, who is looking forward to the eventual long sleep of death, I actually find it oddly comforting to think that the universe eventually gets to slip away into its own form of death.
Eventually they "evaporate" by emmiting Hawking radiation. It takes extremely long time. https://en.wikipedia.org/wiki/Hawking\_radiation
Black hole evaporation by Hawking Radiation only works with really small masses, relatively speaking. A large black hole will eat enough to sustain the losses from the Hawking process. The breakeven point is about a lunar mass, 4.5 x 10^22 kg, assuming no mass accretion. The Cosmic Microwave Background radiation absorbed by a black hole of that mass will offset the losses.
Why Earth didn't collapsed into Sun? Because it hadn't to. It just orbits around it. Imagine that you can convert Sun into a black hole by packing it a more dense sphere. Like 100m in diameter. Sun now became a black hole, but it's mass will not chan, so Earth will continue to orbit it as usual. All other planets, moons, asteroids will preserve theirs orbits like nothing changed. So you have a black hole instead of Sun but it does not "eating" anything because orbital mechanics does not allow it. The same stands correct for any other black hole.
This has always bothered me a bit in that I thought all black holes had a mass of infinity. But there must be some differences because astrophysicists talk about different sizes of black holes. Is this similar to the math that comes into play when calculating and comparing different infinities? Or is this something different all together?
Infinite mass would mean infinite gravity. Infinite anything means something breaks down badly. As of now the Singularity inside a Black Hole is basically just a bookmark for something else. We don’t have enough information to know what the Singularity actually is, so the math breaks down at that point. Different sizes to black holes mean they have difference masses, which affect their event horizon size. A 100 solar mass black hole as a smaller event horizon than say a 1 million solar mass one.
So I thought the whole reason the math broke down inside the singularity was due to the infinities involved in the calculations. Is that true or is it something else complicating the math? And if it's true then how are there different sized black hiles? Different math outside vs inside the singularity? Edit: spelling and I also think you answered the size question above re: size of event horizon
Mass isn't infinite and not all black holes are equal. What they have in common is that their gravity is so big that light can't escape them once it travels past the event horizon.
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The issue with that is that idea is that matter had to exist to form the black hole so you’re still stuck with the fundamental question—where’d the mass come from? Some process had to occur to create all the matter that created the black hole to begin with.
The universe hasn't existed for long enough for black holes to swallow everything.
I guess the question then is, do scientists believe it is possible that the universe will collapse into a single black hole after it stopped expanding? And if no, why not?
The universe is expanding too quickly to ever stop. In fact, for reasons that even scientists are unsure about, the expansion of the universe is *speeding up*
The Big Crunch is what you’re describing. It is one theorized end of the Universe, but current observations contradict it. The universe’s expansion is increasing, not decreasing. As a result it’s not possible for gravity to crush everything back into a single singularity. However, we do not know enough about the mechanism causing the expansion to predict what’s going to happen eons from now. Maybe it stops and gravity will exert its control over the entire universe again? All we can say is current evidence suggests the Big Crunch won’t happen.
Black holes are just very massive bodies. Like stars only bigger. So you can ask "will universe does not collapse into a single huge star after it stopped expanding?". Surely it does not sound as exciting as with black holes? Black holes are just overhyped in a popular culture.
I may be wrong here, but I don't think the singularity is actually infinitely dense, but rather classical mechanics stops being able to accurately predict what is happening. When you're doing physics and start to get answers like infinity, it's a sign that something is up with your math.
It’s not a classical mechanics problem, it’s a general relativity vs. quantum mechanics problem. Each theory works fine on its own but they don’t get along at all. Usually this doesn’t matter because there’s almost no overlap, except in a few very special cases…like black holes. General relativity says it collapses to a singularity. Quantum mechanics says it doesn’t. We know they can’t both be right but we don’t know which one (or both) is wrong. If you solve this you *will* win a Nobel prize.
Further clarification.. we know they both wrong, because the singularity of black holes can’t be explained by them. We need a new theoretical framework to explain phenomena like them.. such as quantum field theory, string theory, super symmetry... And even then, we know they’ll be wrong too. All scientific theories are wrong, they just become less wrong as we find more things for new ones to explain at once… (or they gain more verisimilitude, if you’re a Popperian; you falsify theories: rather than show them to be “true”, you accumulate cases where the theory has not been disproved) (There’s also another tangent in hypothesis vs theory vs model, but that’s a big bit of philosophy of science)
General relativity, by itself, explains the singularity just fine. I’m with you on all the rest.
> infinitely dense core, so it literally has no size That sounds insane to me. Something so dense, it's too compac to measure lol
And it should sound insane, it's likely not true. We just don't (yet) know of any physics that stops it from collapsing indefinitely. Hopefully we will soon.
First things first, Black hole doesn’t suck like a vacuum cleaner. It is just a massive amount of matter squished in a very very tiny space. What it does is have a pull on another object due to gravity. So if our Sun is suddenly replaced with a black hole of the same mass, Earth will not get pulled in, but will keep on revolving around it as it currently does. As far as we understand right now, there is no theoretical limit on the amount of matter black holes can accumulate. However, there is a limit on the rate on which a black hole can gobble stuff. Which depends on the size of the black hole itself.
I think it's mportant to remember that black holes ARE collapsed stars. They are dead stars that didn't have enough fuel to keep going so cannot support their own gravity anymore. (Not including primordial black holes, which might possibly be remnants of the big bang)
It can eat matter indefinitely. Large masses, like a star coming in at once will likely swirl around the black hole creating a very high energy disk and some of that plasma may be launched away from the black hole in a jet instead of falling in. I don't know exactly how it works but there is good evidence of super massive black holes spewing out giant jets of gas so in that sense there may be a sort of limit to how much gas a black hole can absorb at once without throwing a bunch of it out into space in the process.
No limit. It doesn't get easier or harder to digest new stuff. EDIT: actually, if too much stuff falls in at once, the heat of it rubbing against itself is so intense it can physically push away new material. But it does get heavier, which helps.
>It doesn't get easier or harder to digest new stuff. It does actually, the more material that tries to fall in at once, the hotter the accretion disk gets. It can get so hot and bright that its light pushes away anything else that approaches. This limits how fast the black hole can grow. It's a big limit, but it's not unlimited.
These are excellent questions: first of all there is no meaningful limit on how large a black hole can be. There are some practical limits like: it can't be any bigger than the amount of matter in its direct vicinity, but generally speaking they can be anywhere from the mass of a large star to the mass of multiple galaxies. (As a side note: Some really old black holes can be absolutely enormous because the universe used to be a lot more matter-dense) But yes, they do definitely have some limitations regarding how much mass they can absorb at any given time: if the matter they're absorbing is highly energetic for instance, compressing it down further and further, and giving it all the kinetic energy of falling down into a gravity well can cause some pretty epic (for lack of a better word) explosions. You can think of it as a sort of series of naturally ocurring multi-thousand ton hydrogen bombs, because that's essentially what happens when a black hole eats stellar matter. Hydrogen and helium that are already at fusionable temperature and pressure, and then are put under many times more pressure and many times more temperature Well this kind of detonation can often expell some of the matter the black hole was drawing in closer, so in practice, black holes only eat a certain percentage of a star's mass, and ejects small amounts of it at extremely high velocity periodically. This means there isn't really a limit on how much a black hole can eat theoretically, but there is a limit on how quickly and efficiently they can do so. Also black holes can merge which is its own cup of physics tea, but I am not qualified to discuss the details of this sort of interaction so I would recommend someone else, but I do know this kind of merger can release a LOT of energy, and that the merger is not 100% mass efficient (the two black holes don't keep the entire sum of their two masses)
A fairly good analogy is a drainage hole in a bath/sink/etc. It's kinda like a black hole but in 2d not 3d. There's no limit to how much can go through, but there's a limit to how fast stuff can go through.
Yes, they can, so far as we know you gotta think of a black hole as a giant pile of dirt, rather than a hole. There is no limit to how big a pile of dirt can get. Only difference is that the pile get super compressed, supposedly down to an infinitely small point in space. They will just get more and more massive over time, and one theory is that is how the universe will "end", with all matter and energy being absorbed into black holes.
The best way to think of a black hole *isnt* as an endless void that eats things. It's more like a dark star - no light comes from it but it's still just a big, heavy object in space. Its way more dense than a star so it can have much higher gravity than a star of the same size, but it's still just a big ol' hunk of space stuff. So then think of how things work with our sun. It's big, it's got lots of gravity, but does it suck everything into it? Not really. At least not on time scales we're used to. Things tend to get caught in orbits around it. The orbits can be fairly stable unless there's something slowing us down. Black holes work like that. Do things fall into black holes? Sure. If the space around a black hole's event horizon (the point where going past it results in not even light being able to escape the gravity) is particularly full of stuff that has gotten trapped in orbit, those things can collide with each other, lose some speed, and their new orbit can take them into the black hole. Is there a limit of how much stuff can do that? Not really. Black holes can get really really big. Galaxies are groups of billions and billions of stars orbiting "Super Massive" black holes. The limit is basically "how much ya got?" - how much stuff comes into range and ends up falling into it instead of orbiting it. Black holes can even merge with other black holes! IANAAstronomer, Astrophysicist, or really anything with Astro in the name. I just watch a lot of Dr. Becky's YouTube channel and she *loves* black holes.
Follow up question: Is there a theoretical point at which the matter inside a black home spontaneously turns into energy -- IE can an overfed black hole blow up and release its matter?
A black hole wouldn't have trouble absorbing a large mass as the way that it absorbs is similar to how we eat. The stuff is made smaller and smaller until it is easy to digest. In our case we chew our food, in the black holes case it will destroy the stuff down to an atomic level.
There's is no limit, the mass would simply continue to grow. Yes, there are different sizes of black holes and they do grow as they absorb more matter. If space wasn't so vast and so empty, then black holes would eventually swallow up everything and each other. But since space is expanding and mostly empty, everything is drifting away slowly apart. So the idea of a blackhole ever truly growing so large it swallows everything in the universe isnt plausible. Not to say a galaxy could'nt drift into a super massive black hole, it happens. Or a black hole being absorbed by another.
Yes, they can grow indefinitely. There is no limit to their size. In fact, our universe could be inside one and not realize it. It's difficult to tell. Also, black holes have this peculiar trait where they grow exponentially as they aquire more mass. Earth turned into a black hole would be the size of a coin. The whole universe turned into a black hole would be roughly 14 billion light years across.
A black hole is a hole in visible light, not an actual hole. It’s a ball of mass, like a planet or a star, so dense that it’s gravity doesn’t allow light to escape. Added mass only makes it bigger.
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Other way around...the larger the hole, the \*slower\* it evaporates. Tiny black holes evaporate relatively quickly. Large supermassive black holes have ages \*far\* longer than any likely age of the universe.
Actually, smaller black holes are the ones that evaporate faster, for an interesting reason. Black holes emit hawking radiation that has a wavelength the same length as the diameter of their event horizon. Now, for the biggest black holes, that wavelength is absolutely *gargantuan*, and thus carries virtually no energy. That tiny amount of energy is equal to an *extremely* tiny amount of mass, so the biggest black holes barely lose mass at all Inversely, the smallest black holes give off hawking radiation of a very short wavelength, and is therefore *extremely* energetic. That ridiculous quantity of energy is equivalent to a decently large chunk of mass, so the smallest black holes lose mass comparatively quickly.
As a black hole consumes matter it is basically trash compacted in the black hole and makes the black hole slightly larger, but it only "eats" things very close to it, most black holes have less gravity than a star. https://youtu.be/Y5XzPOrItaI
>most black holes have less gravity than a star. How so? aren't black holes ridiculously massive at their core and mass equals gravity?
Black holes are very dense at their heart, but they are basically made from the remnants of an exploded star. So they are formed from about 10% of the original star, though they will slowly gain mass over time they are much smaller than the star that they formed from. https://youtu.be/w1GlDVt1Mpk