You are talking about the accretion disk and Hawking radiation. These are both occuring near but outside the event horizon, influenced by the nearby black hole

No, I am not. I am referring to the collapse event that is before it's actually a black hole. It's a matter of dissipation. As the collapse happens, the heavier elements break apart to neutrons thus imparting the momentum to a smaller particle which means it has a much higher velocity so that it can escape. 15 minutes later, 1/2 the escaped neutrons not stablilized by the degenerative neutron cloud become hydrogen. Basically, it reforms Hydrogen from iron. In doing so, it allows kinetic energy to take over the collapse and blow it apart such as a super nova. The theoretical black hole requires more mass, but if it does not happen instantaneously, it has to happen quicker than the dissipative effects. All before it's actually a black hole.

So if they model a black hole with bose-einstein condensates, they have to stablize it or it collapses and end up with particle jets. On the lab scale of things, a stable containment can be acheived with magnetic containment and the cooling is by allowing the hottest particles to escape. This way, they can achieve ultra cold temperatures by some particle picking up a little more energy than another and escaping and leaving the cooler particle.

Now, how would this happen on the large scale? Consider your containment as gravity. Particles begin escaping which cools the matter even more but the collapse increases the heat. In the lab, they don't need to worry about additional collapse because it's not trying to go critical on a super massive scale. If it were, the jets would begin to increase exponentially. Ever seen a super fluid pop? There's no going back. Think back to the super nova now and why it explodes. The collapse is not quick enough to form a theoretical black hole and it gets turned into kinetic energy.

This is why I say the collapse has to be instantaneous. It has to overcome the dissipation of the particle jets as heat is generated in the actual collapse. For it to be nearly instantaneous, it would require more mass than our moon which is what a theoretical small black hole is. There is simply not enough matter to do it.

Work has been done on how much mass one must start with to get a black hole as opposed to one of the other possible "corpses" like white drawfs and supernovae. I'm not sure what they are, but I think it was something on the order of 5 solar masses while in the main sequence (and about 2 solar masses when collapsing).

Nothing with the mass of the Moon will naturally collapse into a black hole, but maybe a 5-solar-mass star crammed into the Moon's volume would?

Sorry, I don't have the time for in-depth research right now to translate into qualitative terms.

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No animals were harmed in the making of the above post... much.

To replay what I've read about it (I'm sure you'll tell me if I'm wrong):

Hawking radiation will eventually cause any black hole to evaporate, but "eventually" is an unimaginably long time for a large hole. It's a question of the curvature of the event horizon, i.e. the size of the hole.

Small black holes have steep curvature and exert much more effect on the nearby matter/antimatter particle pairs that pop spontaneously into existence throughout space. The particle pairs can do this without violating conservation of energy since their combined energy is zero.

The antimatter particle falls into the hole preferentially, contributing to its evaporation. The matter particle tends to remain outside where it can fly away. This the basis of Hawking radiation and the reason why "black holes are white hot", as Hawking says, due to a flood of energetic matter particles streaming away from a small hole.

Very small holes such as any created in the big bang would already have evaporated, ending in an explosive reaction at the very end and producing a burst of gamma rays. Large black holes will long outlast the stars.

This is mostly in line with what I've seen on it, except that it doesn't matter which of the virtual particle pair falls into the black hole, both have positive mass.

A pair of virtual particles pop into existence, flying away from each other. The electrical attraction makes them slow to a stop then fall back into each other and annihilate. Think of it from a different perspective: what makes an antiparticle an antiparticle? It is spinning in the opposite direction.

If you can picture a normal particle travelling backward in time, it would appear to have an opposite spin and thus be an antiparticle. Now imaging a particle moving in a tight circular orbit. Circles are two-dimensional. If one of the axes of that plane is the "time" axis, then from a typical three-dimensional viewpoint you will see the particle moving forward in time along a semicircle then the same particle moving backward in time along the second half of the circle. While the particle is moving backward in time, it appears to us as an antiparticle. There is apparently evidence to support the existence of these virtual particles.

If the world line of a black hole's event horizon perturbs this happy little circling particle, it flies off and the black hole has lost a tiny bit of its energy in the process. We see the particle "come from nowhere" and call it Hawking Radiation (which has not been directly observed, but it neatly wraps up some conservation issues if it exists).

I don't really understand why these particles would exist, and why they wouldn't just fall into the black hole. You'll have to ask Professor Hawking about that.

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No animals were harmed in the making of the above post... much.

If you can show me a formulation for a black hole that takes into account matter ejection during the cooling process, I'll give it cosideration. If it only considers cooling radiation, it's not complete.

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TEAM
LL

If you can show me a formulation for a black hole that takes into account matter ejection during the cooling process, I'll give it cosideration. If it only considers cooling radiation, it's not complete.

I did a quick search and found this paper on hypercritical accretion leading up to the formation of a stellar mass black hole. I think it only applies to binary systems with one black hole and one star, but I didn't have enough time to digest the whole thing and make a qualitative case for it. The jist is that the gravity-induced inflow bats back anything ejected from the collapsing star.

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No animals were harmed in the making of the above post... much.

If you can show me a formulation for a black hole that takes into account matter ejection during the cooling process, I'll give it cosideration. If it only considers cooling radiation, it's not complete.

I did a quick search and found this paper on hypercritical accretion leading up to the formation of a stellar mass black hole. I think it only applies to binary systems with one black hole and one star, but I didn't have enough time to digest the whole thing and make a qualitative case for it. The jist is that the gravity-induced inflow bats back anything ejected from the collapsing star.

That is an interesting paper. I plan on reading it again in closer detail but with the first initial read, it appears that the jets and outflows that they talk about are from the accretion disk and not the neutron star itself. The accretion disk being the part falling into the star. Although, they did make a mention of of outflows from the neutron star affecting the outflows from the inner disk.

Alternatively, outflows may arise predominantly from the inner disk. In this case, the energy feedback into the common envelope from outflows originating deep in the neutron star potential well could be highly significant.

So, it's given an honorable mention but not directly dealt with.

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TEAM
LL

I think the problem is not that a theoretical black hole can't be stable. It very well could be stable. It's the activation energy to actually get to a black hole.

...........<E_activation energy>=huge
...............--
............../..\\
............./....\\
............/......\\
.........../........\\--<E_blackhole>
........../
........./
......../
......./
<E_matter>

The point here is that if the black hole is stable, it's not enough to say it meets the requirements of the Schwarzchild blackhole or satisfies the metric. You have to get to it. The diagram above is to represent an activation energy needed to take some amount of matter at energy <E_matter> to <E_black hole>. The problem is getting that equation correct. There are too many possible variables to know for sure if it's correct.


The reverse might be.

................<E_activation energy>
...................--
................../..\\
................./....\\
................/......\\
.............../........\\
<E-blackhole>...\\
..........................\\
...........................\\
............................\\
.............................<E_matter>

The thing that would make a black hole stable is if the activation energy to blow it apart is higher than it's current energy even though the <E_matter> is a lower energy level.

My assertion is that the <E_activation> has not been properly dealt with. The equations tend to point out that a black hole is theoretically stable, but if the activation energy is greater than the total energy of the universe, the point of the black hole being stable is moot because it'll never happen. Proving that it can be stable at 1000 solar masses is not proving that it can happen because the activation energy might simple be too high.

Like Stephen Hawkings said himself, since you are not directly probing the black hole, you can never be sure that it ever really formed. If it looks like a duck, walks like a duck, it could still be a goose.

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TEAM
LL

The "density" of a black hole (It's mass divided by it's Schwarzschild volume) evalutes to this:

(1.8x10^16 g/cm^3) x (Msun / M)^2

Don't shoot me if this equation is wrong, I grabbed it from here.

The density of a neutron star is about

3 x 10^14 g/cm^3

If we postulate that a neutron star won't collapse, no matter how massive it is,
and look at one that is constantly picking up mass from a companion star,
then this neutron star can only grow until it's mass M has reached the mass of a black hole with equal density. After this point it will vanish into a black hole:

(1.8x10^16 g/cm^3) x (Msun / M)^2 = 3 x 10^14 g/cm^3

(Msun/M)^2 = 3 x 10^14 / 1.8x10^16

(Msun/M)^2 = 0.017

Msun/M = 0.129

M = 7.75 * Msun

This transition is instantaneous and doesn't require an inifinitesimal activation energy since no creation of an infinitely small black hole is required for it to happen.

Regards Hans

P.S:
This calculation assumes that the neutron star has uniform density.
In reality it's core will be more dense and the collapse happens earlier and more violent.

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You still have to explain the increase in density. When you increase the density, the kinetic energy/temperature that needs to be released will grow exponentially. Thus, you need a way to cool it so that it can collapse before it blows up or blows off too much matter. This is typically done with a radiation density but does not take into account matter dissipation.

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TEAM
LL

You still have to explain the increase in density. When you increase the density, the kinetic energy/temperature that needs to be released will grow exponentially. Thus, you need a way to cool it so that it can collapse before it blows up or blows off too much matter.

There would be no increase in density (as viewed from the outside).
The newborn black hole has the same radius and density as the hypothetical neutron star.

Once you're inside the Schwarzschild radius, things get weird.
I don't even know if the neutron star would collapse once the Schwarzschild radius raises above it's surface.

Maybe Octagon can add some insight here.

Regards Hans

P.S: Since matter and energy are equivalent, it wouldn't make a difference if things heat up inside the Schwarzschild radius while potential energy turns into heat.

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Chandra solves black hole mystery

The way in which black holes suck in matter from neighbouring stars is a fundamentally magnetic process and not just caused by gravity. That's the conclusion from new measurements of the X-rays emitted by the gas surrounding a nearby black hole in the Milky Way. Although predicted by theory over 30 years ago, this is the first time that this effect has been seen. The result -- based on measurements from the Chandra X-ray observatory -- could affect theories on how matter falls onto black holes and other compact objects (Nature 441 953).

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TEAM
LL

There would be no increase in density (as viewed from the outside).
The newborn black hole has the same radius and density as the hypothetical neutron star.

Once you're inside the Schwarzschild radius, things get weird.
I don't even know if the neutron star would collapse once the Schwarzschild radius raises above it's surface.

You held the radius the same and packed more matter in. You have to account for the compression of that matter.

Maybe Octagon can add some insight here.

Regards Hans

P.S: Since matter and energy are equivalent, it wouldn't make a difference if things heat up inside the Schwarzschild radius while potential energy turns into heat.

But they are different when you measure them and there is no reason to meausure just radiation and not measure the matter coming off. You cannot say, this much radiation came off and a black hole formed without taking into account how much matter spewed off because that could thwart the density/heat problem. It has to be dense enough and cool enough.

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TEAM
LL

You held the radius the same and packed more matter in. You have to account for the compression of that matter.

I guess that's the key point you're touching here :o)

The "density" of a black hole (as seen from the outside) actually decreases as it's mass M grows:

rho = (1.8x10^16 g/cm^3) x (Msun / M)^2

If you double the mass of a black hole by throwing stuff into it, it's density will decrease to 1/4.

You can get black holes of arbitrarily low density by doing so.

Regards Hans

P.S: The surface temperature, as indicated by the Hawking radiation, also drops when a black hole grows.

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You held the radius the same and packed more matter in. You have to account for the compression of that matter.

I guess that's the key point you're touching here :o)

The "density" of a black hole (as seen from the outside) actually decreases as it's mass M grows:

rho = (1.8x10^16 g/cm^3) x (Msun / M)^2

If you double the mass of a black hole by throwing stuff into it, it's density will decrease to 1/4.

You can get black holes of arbitrarily low density by doing so.

Regards Hans

P.S: The surface temperature, as indicated by the Hawking radiation, also drops when a black hole grows.

1. you just started with a black hole.
2. the problem is to get to the black hole, not start with one.
3. Hawking radiation is not proven, and is only for black holes, not the formation of a black hole.
4. It's not enough to say it meets the requirements of the black hole. You have to make the transistion from the set density to the varying conditions of the black hole.
5. Neutron stars can't have more than 3xM_sun because at that point the degenerate neutron cloud stabilizing pressure cannot prevent collapse. Thus you have to some how magically get from M_n <(less than) 3xM_sun to your theoretical 7.75xM_sun.

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TEAM
LL

I'm really glad I clicked on the BlackHoles site you referenced...BUT, did you see that black holes is just one small part of HubbleSite.org...? The entire site is terrific.


<---Richard Feynman

Team Richard Feynman

Some models for black hole formation predict that the back hole is the interior remnant of a supernova (kind of like a "white dwarf and planetary nebula" on steroids). Presumably, these models assume any black hole we see today has either recaptured its castoff material, or is so old that its castoff material has already been assimilated into nearby stars and nebulae.

That does seem a bit too convenient.

Since neutron starts explode into supernovae due to runaway reactions that only take a fraction of a second, it is reasonable to deduce that neutrons stars that collapse into black holes also do so in a fraction of a second. The "average case" where a white dwatf simply cools into a black dwarf with no climax is predicted to take longer than the presumed age of the Universe (13.7 billion years). I saw presumed because I want to include Modified Steady State models of the Universe.

If the Universe is orders of magnitude older than 13.7 billion years, black dwarves could account for some, but not all, of the observed actions attributed to black holes.

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No animals were harmed in the making of the above post... much.

Supposedly, although it's "stable" at 7.75 solar masses, to actually form a black hole in the first place, it takes 25 x M_{sun} that is 25 solar massses. If it's exploding at 3 solar masses how can one account for the the 22 solar masses disparity? You would need 9 of the largests neutron stars colliding at one moment in time.

Do you have links to the models that you're talking about?

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TEAM
LL