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Wikipedia says,

A black hole grows by absorbing everything nearby, during its life-cycle. By absorbing other stars, objects, and by merging with other black-holes, they could form supermassive Black-holes

  • When two black-holes come to merge, don't they rotate with an increasing angular velocity as they come closer and closer (how does it from a neutron star? I mean, who's powerful?)

And it also says,

Inside of the event horizon, all paths bring the particle closer to the center of the black hole.

  • What happens to the objects that are absorbed into a black-hole? Which state are they really are now? They would've already been plasma during their accretion spin. Would they be on the surface (deposited), or would they still be attracted and moved towards the center? If so, then the surface of black-hole couldn't be a solid.
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2 Answers 2

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An object isn't necessarily heated to a plasma when it falls into a black hole. With quasars matter spirals down towards the event horizon so both it's speed and density increases, but this doesn't heat it directly. It's because matter interacts with the other matter around the event horizon that you get collisions and heating and the spectacular X-ray emission.

By contrast the black hole at the centre of our galaxy is thought to be fairly quiet because it's already gobbled up all the matter in it's vicinity. If you jumped into it you'd probably make it through the event horizon unharmed and it would only be near the singularity that tidal forces squished you.

You need to bear in mind that once matter has passed the event horizon it's fall to the singularity is very quick, so there isn't very much matter within the event horizon that hasn't already fallen into the singularity. What happens to the matter at the singularity no-one knows.

Response to comment: my point is that an acretion disk isn't a feature of all black holes. Accretion disks only form where a black hole is actively swallowing matter. Also accretion disks will form around any heavy object. Arguably Saturn's rings are a form of accretion disk with the matter in them eventually falling into Saturn.

My other point is that for matter falling into a black hole nothing special happens when it crosses the event horizon. If you were falling into a black hole then you wouldn't be able to detect when you had crossed the event horizon. So if you had been heated up by friction in an accretion disk before you hit the event horizon you'd be in pretty much the same state after you'd crossed it.

The state you're in, whether it's plasma or not, is dependant on how much you got heated up as you fell through the accretion disk (if an accretion disk is present) and is not anything specifically related to the presence of an event horizon.

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Sorry. But, could you please elaborate your answer for my first question to provide a better understanding. Why do you say "not necessarily heated to plasma"... While spinning in the accretion, don't friction heat the objects to plasma? –  Waffle's Crazy Peanut Aug 30 '12 at 0:23
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Wikipedia says it's not a state of matter, but a property of spacetime.

The gravitational singularity predicted by general relativity to exist at the center of a black hole is not a phase of matter; it is not a material object at all (although the mass-energy of matter contributed to its creation) but rather a property of spacetime at a location. It could be argued, of course, that all particles are properties of spacetime at a location,[13] leaving a half-note of controversy on the subject.

http://en.wikipedia.org/wiki/State_of_matter

Given the "half-note of controversy on the subject" and the valid objection to the suggestion that black holes are not states of matter, I propose we call it Singularium.

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The text you've quoted mentions about the mathematical singularity which isn't matter (yeah, but) the question which I intended to ask then, was about the form of matter that makes the black hole itself, not the singularity! –  Waffle's Crazy Peanut May 9 at 17:03
    
That is not what you asked. The title of your question is "Black-holes are in which state of matter?" Further to my point, you ask "What happens to the objects that are absorbed into a black-hole? Which state they really are now..?" There is no "surface" of a black hole. It is an infinitesimal point. –  turibe May 9 at 17:32
    
(sigh) Blackholes aren't infinitesimal. They're finite in size, and have a finite mass. You're talking about the center of the blackhole (the singularity) where the laws break down while I'm talking about the entire blackhole! –  Waffle's Crazy Peanut May 9 at 17:54
    
You're right about the singularity vs black hole. I was editing my comment to that point, but my time to do so expired. Your question is very unclear. I believe now that you're asking what is the state of matter between the event horizon and the singularity. But I could not have discerned that from your question. –  turibe May 9 at 18:02
    
"Would they be on the surface (deposited) or would they still be attracted and moved towards the center..?" Inside the event horizon attraction towards the singularity is inevitable. –  turibe May 9 at 18:03
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