Quote by twofishquant
It's possible once you reach GUT densities. On the other hand there are some constraints that tell you what is likely to happen.
The thing about degeneracy pressure is that you can show that degeneracy pressure always disappears if you crank up the gravity enough. So even if the fermions stay fermions, the degeneracy pressure disappears.

the degeneracy pressure doesn't really disappear i think, its just that there's really enough energy to force the fermions into very high energy states close to each other (or inside each other). if it did actually disappear i'd think there'd be many problems with even chemistry that we could observe.
Quote by twofishquant
No degeneracy pressure. I walk on a floor of wood, I don't fall through the floor. If I create a floor of photons, then I can't walk on it.
The problem with nondegeneracy pressure is that it doesn't generate much force. If I take a gas, and increase the density, the pressure only goes up slightly, which means that you don't have much force to resist gravity. If I take a solid, and increase the density even slightly, the pressure increases by a huge amount. So while photons do exert pressure, it's the dependency between density and pressure that matters, and for nondegenerate matter even if the pressure is high, increasing the density only increases the pressure slightly.
As things go relativistic all particles start behaving more like photons, so once the floor of wood goes relativistic it's like a floor of photons (i.e. you can't walk on it).
On thing about these sorts of arguments is that they are independent of the details. We don't know exactly at what mass neutron stars will collapse, but if special relativity is correct, then at some mass they'll collapse.
Also you can put upper limits. If you assume an unknown particle that increases the number of energy states available, so any unknown particle is going to decrease the critical mass. If you look at the estimated critical mass of neutron stars over time, it's gone down, because as you discover new particle interactions, you make the material softer.
One other note, is one big difference between neutron stars and black holes is that neutron stars have a hard surface whereas black holes don't. What this means is that if you look at a one solar mass object, you see big radiation flashes whereas with eight solar mass objects you don't. The explanation for this is that with neutron stars, sometimes matter will bunch up and hit the surface and when that happens there is a huge radiation burst. With black holes, there is no surface, so no radiation bursts.

accretion disks, converting angular momentum and gravitational potential energy to radiation?
as things go relativistic, can we think of it as "thermalizing" the degenerate materials such that they attain a more "Boltzmanlike" distribution?