Hans

The recent topic on quark stars has rekindled an old curiosity of mine, and that is the question of what happens to matter that has fallen into an event horizon.

My confusion is fostered by statements like "at the center of a black hole is a singularity where density is infinite and physics as we know them break down." From this description, combined with others, I take it that the singularity is believed to be subatomic in size and that the distance between the singularity and the event horizon is empty with the exception of any material being drawn into the singularity. The material would be flowing inward as opposed to being held up away from the singularity such as by some highly dense object.

My question is: Do we have enouph understanding of matter to pressume that:

a) It is possible to compress matter to a size that is smaller in diameter than the event horizon such a large mass would produce?

b) There is no other point below the diameter of the event horizon where it is impossible for matter to be compressed into a higher denstity or smaller diameter?

I guess it comes down to wondering if it can be successfully theorized that infinite density is possible. Or if instead it is more reasonable to pressume there is some finite limit to density somewhere above, at, or below the event horizon. Or is it pretty much unknown what happens after the degenerative pressure is overcome?

liquid

Some of your points are a little unclear (but then I am very tired right now!). I will answer what I can.

"I guess it comes down to wondering if it can be successfully theorized that infinite density is possible."

It can be be successfully theorized. That is exactly where the idea of black holes comes from, not the other way around. They were predicted, and only afterwards was the evidence found.

As to whether the infinite density actually exists in reality... that is not so certain. Many theoretically infinite things never get there in practice (any asymptote you care to name!). I am not even sure if things beyond the event horizon exist in a conventional sense.

As for point a), I don't quite understand it. It is certainly possible that you can compress matter smaller than the event horizon, if that is what you mean. As for the singularity itself, which is what you wrote - I don't think that for an outside observer that anything ever enters the singularity - time slows down looking in. But I am not quite up to speed on this so might be wrong.

And b)? Well, density is the key, not diameter, and you cannot exceed an infinite density...

Undercurrent

It is, incedentally, one of the strongest criticisms of the concept of a black hole, that in every other field, if there is a singularity in the equations it is assumed to be the fault of the equations, not the universe, while in the black hole, it is proposed to be an actual singular point in the universe.

m.

Steven S

I think this question is posed poorly. The event horizon has the radius given by twice the mass of the mass contained within it. For example, if the sun was compressed into a black hole the event horizon would be 3 km. What the event horizon does is separate the spacetime within from the spacetime in the rest of the universe. As for b) I'm not quite sure what you are asking.

Steven S

Answerer

Actually, many physicists are unhappy with the existence of singularity which is a point of infinite density and breaking down of all physics laws. This is why some of them are creating the string theory for , to remove singularity from their equations in general relativity and to obtain a better understanding of the 'physics' inside a black hole. So, I think that we just have to wait for some times, before they could came up with a proper string theory.

Late_Cretaceous

I think he may be asking 'what state is matter in a black hole in'. I have wondered this myself. The author of a book I am reading claims that if all the matter in the universe were to be compressed to the density of an atomic nucleus it would occupy a space equivalent to the solar system. That would probably be like neutron star or perhaps a quark star. But what of a black hole. Are the quarks still quarks, or have they been squeezed together so much that there are no longer any sub atomic particles as we know them?

elwoodblues

"My confusion is fostered by statements like "at the center of a black hole is a singularity where density is infinite and physics as we know them break down." "

No wonder you're confused. You don't seem to know that the above phrase is physicist code for 'We don't know what the fuck is going on, and it freaks us out, man!' Of course, that doesn't look very good in a peer-reviewed paper, so they stick with the code instead.

fando

If the singularity concept bugs you, perhaps you'll find solace in the Gravastar theory. Instead of mass collecting into a singularity, a Gravastar has mass condensed into a thin spherical shell. The interior of a Gravastar is normal space, but the gravitational attraction is towards the shell, which is made up of an "ultra-relativistic fluid of soft quanta." The reason the shell forms instead of a singularity has to do with certain quantum effects on gravity which I don't fully understand.

I'll attempt to explain anyway: the solution to Einstein's field equations of a heavily curved spacetime changes when certain quantum mechanical considerations are factored in. The solution yields a pecuiliar form of gravity within an event horizon, termed a "gravitational bose einstein condensate", which generates an outwards pressure on infalling matter. So the net effect is that all matter ends up part of a shell where the inward and outward forces balance (originally the Event Horizon of a Black Hole). The shell is a super-rigid fluid with interesting properties (the speed of sound is equal to the speed of light). As the Gravastar accumulates matter, the interior generates more outwards pressure, which in turn increases the radius of the Gravastar's shell.

In addition to being more aesthetically pleasant than singularities in spacetime, the Gravastar theory is free of certain knotty problems that plague the Black Hole theory, such as the information paradox. (A Black Hole contains many orders of magnitude more entropy than the originating star could possibly have. Where did this extra entropy come from?)

Gravastars are an area of active research. Here's the <a href="http://xxx.lanl.gov/abs/gr-qc/0109035" target="_blank">preprint on Gravastars</a>. You can google for more accessible articles.

MortalWombat

Gravastar... sounds like a good name for the next Daimler-Chrysler concept vehicle.

Hans

Let me try to clear up the ambiguity in my questions.

I understand that quarks are believed to be the elementary particals that make up all matter. I also understand that it is believed there are no other smaller elements of which quarks are composed.

Take one million solar masses worth of pure quarks and compress them together so that they are in continuous contact with each other and have zero kinetic energy relative to each other. Just a big ball of quarks all tightly packed together like a balloon tighly filled with marbles.

Now a black hole having a mass of one million solar masses will produce an event horizon of a predictable radius. We'll say radius equals X.

My question is will my hypothetical one million solar mass ball of quarks have a radius that is equal to, greater than, or less than X?

Regardless of the answer to the question above my next question still remains: How much force is required to compress my ball of quarks into a smaller radius when all the quarks are already in contact with one another?