B If Quark stars exist why do Neutron stars become Black holes?

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wolram

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From Wikipedia:
Quark-degenerate matter may occur in the cores of neutron stars, depending on the equations of state of neutron-degenerate matter. It may also occur in hypothetical quark stars, formed by the collapse of objects above the Tolman–Oppenheimer–Volkoff mass limit for neutron-degenerate objects. Whether quark-degenerate matter forms at all in these situations depends on the equations of state of both neutron-degenerate matter and quark-degenerate matter, both of which are poorly known. Quark stars are considered to be an intermediate category among neutron stars and black holes. Few scientists claim that quark stars and black holes are one and the same. Not enough data exist to support any hypothesis but neutron stars with awkward spectrums have been used in arguments.

If Quark stars exist why do Neutron stars become Black holes?
 

russ_watters

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If Quark stars exist why do Neutron stars become Black holes?
I'm not sure I understand what one has to do with the other, but still may have some insight...

A black hole is just a thing with an event horizon, not a state of matter. A blob of water floating in space could be a black hole if it was big enough and its own gravity didn't crush it; the density of a big black hole is quite low.

Some scientists are uncomfortable with the idea of all matter in a black hole being crushed to a point. A "quark star" may be an opportunity to suggest a comprehensible non-zero size object exists behind the event horizon (inside the black hole).

If that's the case, you wouldn't say the quark star IS the black hole, but rather that it generates the black hole around it.

[Edit] We often get people arguing that black holes don't or might not exist because we don't know the nature of what is behind the event horizon. I think they miss the point; it could be a singularity, a quark star or a block of limburger cheese. It doesn't matter; The event horizon is what makes it a "black hole".

And why does bypassing that argument matter? Because it stands in the way of considering all the possibilities for what could lie behind the event horizon - including the possibility that there is more than one kind.
 
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I'm not sure I understand what one has to do with the other, but still may have some insight...

A black hole is just a thing with an event horizon, not a state of matter. A blob of water floating in space could be a black hole if it was big enough and its own gravity didn't crush it; the density of a big black hole is quite low.
Size and gravity crushing it doesn't matter. It's the amount of mass that matters. If that blob of water had 20 solar mass and was the size of a baseball it would theoretically become a black hole.
 
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Size and gravity crushing it doesn't matter. It's the amount of mass that matters. If that blob of water had 20 solar mass and was the size of a baseball it would theoretically become a black hole.
And it would not, in the circumstances you describe, be a blob of water.
 

wolram

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Thank you for the replies, most interesting:biggrin:
 
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If Quark stars exist why do Neutron stars become Black holes?
It's interesting actually, or the same question can be expressed by how neutron stars become directly to black holes ? What happens to the neutrons in that process ? Or what happens to the quarks in that process ?

I think quarks are more stable in the neutron form, rather then on their own. This could be the reason maybe we dont see a quark star or the reason of why neutron stars just become the black holes.

Also neutrons are essentially just quarks, so in what type of state they can combine or just resist the gravitational affect ?
 
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Chronos

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The density of a black hole is calculated based on the volume encompassed by its event horizon, which tells you nothing about the density of matter inside the event horizon
 

PAllen

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Size and gravity crushing it doesn't matter. It's the amount of mass that matters. If that blob of water had 20 solar mass and was the size of a baseball it would theoretically become a black hole.
If you had a cloud of the density of air the size of the Milkyway galaxy, it would already be inside its event horizon. You do not need high density for BH. Note, that the overall density of the Milkyway is many orders of magnitude less than air due to the enormous space between objects.
 
If you had a cloud of the density of air the size of the Milkyway galaxy, it would already be inside its event horizon. You do not need high density for BH. Note, that the overall density of the Milkyway is many orders of magnitude less than air due to the enormous space between objects.
I never said density. I said mass. They are two different things. =)
 
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I never said density. I said mass. They are two different things. =)
I think you can safely assume that pallen knows the difference. What he was commenting on was that it's not exactly the amount of matter that matters, it's the amount of space that that matter takes up and that's represented by density. Do you understand what he told you? Forget about how it relates to your comment if that's holding you back from considering what he said in its own right.
 

PAllen

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I never said density. I said mass. They are two different things. =)
I point of fact, density is the issue. Any amount of mass, big or small, can be a BH in principle. The required density is inversely related to mass - the larger the mass, the lower the density at which BH formation becomes inevitable. For 20 solar masses, you would be talking about well over 10 kilometers, not baseball size (which was the comment I originally responded to).
 
I point of fact, density is the issue. Any amount of mass, big or small, can be a BH in principle. The required density is inversely related to mass - the larger the mass, the lower the density at which BH formation becomes inevitable. For 20 solar masses, you would be talking about well over 10 kilometers, not baseball size (which was the comment I originally responded to).
Ah, I see what you're saying now. I was just giving a random number and size.
 
I point of fact, density is the issue. Any amount of mass, big or small, can be a BH in principle. The required density is inversely related to mass - the larger the mass, the lower the density at which BH formation becomes inevitable. For 20 solar masses, you would be talking about well over 10 kilometers, not baseball size (which was the comment I originally responded to).
This thread established that what's inside a BH is irrelevant as long as there is sufficient mass within a small enough volume. (According to Schwarzschild in 1916, the radius of a BH event horizon is about 3 km per solar mass regardless of the BH mass. Surprised nobody mentioned this already.)

Going back to Wolram's original question of whether stable quark-degenerate matter exists, it occurs to me that natural end states of many stars are defined by the degenerate matter they comprise, including white dwarfs (stable, electron degenerate, smaller than the Chandrasekhar limit of 1.44 solar masses) and neutron stars (stable, neutron degenerate, within the TOV limit of around 2.2 solar masses). Current descriptions of more massive post-supernova cores expect collapse to a black hole and the resulting paradox of the singularity -- which can be eliminated if a third, naturally occurring stable configuration of quark degenerate matter forms (the "quark star"), halting further collapse but within the BH event horizon.

Can anyone point to current research on quark degenerate matter and any upper mass limit for quark stars?
 

Ken G

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I don't think quark stars are normally thought of as lying inside black hole event horizons. And as per russ_waters' original point, it wouldn't much matter if quark stars prevented collapse to a singularity if they are inside the EH, since we'd never observe them anyway and to us it would still just be a black hole (they have "no hair", remember). So the actual astrophysical interest in quark stars is for objects that we can see, i.e., a degenerate state of matter that is intermediate to neutron stars and black holes, which exist outside their own EH so are "normal gas" in that sense (just with very odd composition and degenerate thermodynamics). So I would say the answer to why neutron stars can become black holes if they get too much mass, without being quark stars instead, is that quark stars would presumably also have a mass limit-- and it might not be much larger than neutron star mass limits because neutron stars may already have some quark-star-like properties in their interiors. For any pure degeneracy pressure situation, adding mass will reduce the radius, so a black hole is inevitable at some mass, and likely not much more than a neutron star maximum mass which is already not much more than a white dwarf maximum mass.

One can estimate these mass limits simply by noting that when electron degeneracy dominates (neglecting all else, such as strong forces and general relativity), the particles go relativistic (which produces the mass limit) when the mass is roughly the cube of the Planck mass divided by the square of the mass per degenerate particle (and that's not the mass of the degenerate particles, it's the total mass divided by the number of degenerate particles). So all you need to know is how many degenerate particles you have per gram of star. When a white dwarf turns into a neutron star, you might expect about twice as many neutrons as you had electrons, so the mass limit should be 4 times higher. It is not nearly that much because of general relativistic effects, but at least we see why neutron star limits are higher by order unity. For a quark star, using the same simple reasoning, the one expects to have 3 times more quarks than neutrons, so one expects the limit to go up again by a factor of 9. For similar reasons, we'd expect it is actually much less than that, but still an order unity increase.

As for quark stars inside event horizons, the usual interpretation of GR solutions is that no force at all could prevent collapse to a singularity, since the radial coordinate has in essence become a time coordinate and the arrival at the center (or the central ring for a spinning black hole) becomes a geometric inevitability regardless of any forces on the gas. Moreover, if degeneracy pressure is all that holds up a quark star (rather than the strong force that supports neutrons-- that is presumably not sufficient and we have nothing left but quark degeneracy), it is certainly true that degeneracy will never resist the gravity inside an event horizon. That's because degeneracy pressure is just gas pressure, meaning that it is not actually a force on the particles at all, it is merely a reflection of how the particles transport momentum even in the complete absence of collisions, i.e., it is simply the action of particles in free fall. General relativity is all about the paths taken by particles that are in free fall, and they go to the center.
 
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I don't think quark stars are normally thought of as lying inside black hole event horizons. And as per russ_waters' original point, it wouldn't much matter if quark stars prevented collapse to a singularity if they are inside the EH, since we'd never observe them anyway and to us it would still just be a black hole (they have "no hair", remember).
Gravitational waves can pass through a black hole, no? Wouldn't a gravitational wave passing through a black hole get affected differently if the interior housed a rather large quark star or similar, compared to a tiny, nearly infinitely dense region? I'm thinking similar to how light is bent passing through a large vs small cylinder.
 
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Gravitational waves can pass through a black hole, no? Wouldn't a gravitational wave passing through a black hole get affected differently if the interior housed a rather large quark star or similar, compared to a tiny, nearly infinitely dense region? I'm thinking similar to how light is bent passing through a large vs small cylinder.
https://en.wikipedia.org/wiki/Shell_theorem

EDIT: OOPS ... I misread your post
 
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Ken G

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Gravitational waves can pass through a black hole, no? Wouldn't a gravitational wave passing through a black hole get affected differently if the interior housed a rather large quark star or similar, compared to a tiny, nearly infinitely dense region? I'm thinking similar to how light is bent passing through a large vs small cylinder.
One cannot use gravitational waves to probe the interior of an event horizon, even if one had the impossibly difficult sensitivity to do so. The spacetime in there literally only connects to the center, so that's where any waves would go as well. I don't know what a GR solution of a gravitational wave passing a black hole would look like, but my guess would be the best way to describe it is the wave diffracts around the hole, moreso than refracts through it and comes out the other side.
 
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One cannot use gravitational waves to probe the interior of an event horizon, even if one had the impossibly difficult sensitivity to do so. The spacetime in there literally only connects to the center, so that's where any waves would go as well.
I had naively assumed that the ringdown LIGO detected meant gravitational waves could escape the interior, but I get your point.
 

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