so black holes evaporate because of vacume fluctuations near the event horizon. hawking sais that little is known about what happens as the black hole eventually gets smaller and that it probably evaporates completely. I do not follow this logic b/c it seems to me that when the evaporation causes the gravitational strength to diminish it would eventually approach the critical level that caused the collapse initially and what would follow would be some type of inflation in which the strong nuclear force would become stronger relative to the diminishng gravitational force. I know somone has had to think of this before but I have never heard anything about it. What do you guys think?
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Well Hawkings radiation is pretty insignificant in black holes that occur from stellar collapse, realistically they're going to gain much more mass from accretion than they'd lose from Hawkings radiation. For a Schwarzchild black hole the relationship between mass and radius is given by the Newtonian equation: r = (2G/c^2)m or, as G and c are constant, r = k m so you can see the mass and radius are directly proportional, therefore all that will happen when a black hole losses mass is that it's radius will get will get smaller unitl it is so small it can said to of evapourted.
yeah, you are talking about the event horizon size, not the size of the singularity, I'm saying that as the EH gets smaller, (apparent) particle emission increases, making it (EH) smaller and smaller. Soon the EH must approach the critical point just as it did pending the initial collapse and the nuclear strong force of the particles remaining in the singularity should overcome the quickly depleting gravitational force and cause the singularity to inflate again as the strong force takes over again, just as when the gravitational force took over in the initial collapse. am I missing something?
But the singularity doesn't actually have any size whatever it's weight. There is no critical point, however as the event horizon gets smaller the less energy photons need to 'borrow' to quantum tunnel out of the black hole, so Hawking radiation becomes more nad more effective. A black hole less than the size of an atomic nucleus would by radiating a lot of energy and shrinking very quickly and according Hawkins would be indistuingusihable from the time reverse of a black hole - a white hole. There is no lower limit, excepting quatum considerations, for the mass of a black hole.
If there is such a thing as critical limit to the shrinking of the event horizon, than sooner or later we would observe a violent supernova caused at a place where no stars were observed... If there is no such thing as a critical limit and the black hole is allowed to slowly evaporate BELOW the size/mass that would be necessary to create the black hole in the first place, than it would mean that the particles captured by the black hole are not packed in a dense material globe like with a neutron star, but would be actually stored on an other dimesional plane and we are only left with the singularity and the gravitational force that links the singularity to that other plane.....
The point is there is no reason at all to think there is a limit on the event horizon/mass of a black hole. The physics which describes them doesn't have any critical limit and rules out the possibilty of a critical limit.
I think the basic thing that's being miseed is that there is no critical limit for the mass required to create a black hole. There is probably a minimum mass for a black hole to occur from stellar collapse (which is guessed to be about 25 solar masses) and there is a limit on the mass of a neutron satr before it collapse to a black hole (3.2 solar masses) but a black hole, in theory, can be any size when it is created. In the current era of the universe the only forces strong enough to create a black hole comes from the collapse of supermassive stars, so there is a minimum limit to the size of a black hole at creation in this current era. However when the universe was a lot denser it is possible that black holes were created, by density flucations, with comparitvely small masses.
Sorry, I should add the 25 solar masses figure is for the star that forms the black hole, the actual black hole formed would weigh significantly less than this (about 4 solar masses).This is as the star would throw off most of it's mass when it goes supernova.
regarding the star-less supernova I was under the impression that the singularity inside the horizon did in fact have a definate size, according to some sources it would be a few miles (1-10) in radious.
Re: regarding the star-less supernova According to classical theory, a singularity is a point where the density is infinite, meaning a finite mass is compressed to a zero volume. We arrive at infinity in these cases because classical theory breaks down on these scales. A theory of quantum gravity might avoid the need for singularities.
Re: regarding the star-less supernova The black holre singularity has no size, I think you're thinking of the event horizon, a typical black hole (of 8 solar masses) formed by a star of about 50 solar masses would have an event horizon of radius 24km or roughly 10 miles.
no I mean the singularity itself, not the event horizon, a non-rotating black hole could collapse to a point but if it has any angular momentum at all (which would allways be the case in the real world) the collapse would increase the spin (like an ice skater pulling his arms in) and form a disk or ring? I think the matter does not actually go to infinite density, even in a BH I refuse to accept infinity as an answer, but maybe it forms a different state like the newly discovered BEC. Its a shame our technology is so primative.
Yes, a rotating, or Kerr black hole does have a ring shaped singularity, and the event horizon becomes oblate (flattened) like an M+M. But the ring-shaped singularity is still infinitely thin, and has a total volume of zero. _____________________ SF worldbuilding at http://www.orionsarm.com/main.html
infinity Okay, but what do you think the odds of having an infinite density zero volume anomaly are versus a gravitational induced exotic form of matter? because what would be left to maintain the gravitational influence?
