akallen404: Tranquil Hegemony: Lambskincoat: A white dwarf, a neutron star or even a strange quark star are all still made of fermions. The Pauli degeneracy pressure helps hold up the stellar remnant against gravitational collapse, preventing a black hole from forming.

My suspicion has been that the Pauli exclusion principle would prevent the ultimate collapse into a singularity, but the object would still be compact enough to form an event horizon.

Ethan seems to be suggesting that this doesn't apply within the event horizon because no interactions can propagate outward from the center, or even propagate anywhere but to the center, if watching all those episodes of PBS Space Time has taught me anything. So if an electron and a proton fall into the black hole, they can't form a hydrogen atom on the way down because they can't exchange force carrying particles. They can't interact. Okay.

So is he saying that the Pauli exclusion principle operates like a fundamental force? I thought it was an inherent feature of spacetime.

There was a debate a few years ago when filmmakers were using ray tracing and math to create the (now iconic) black hole from "Interstellar." Apparently there are actually a couple of different models for how that would really work out and the one from Interstellar was chosen purely because it looked really cool. Another, more accurate model rendered the event horizon as an ill-defined region where the background is warped and stretched towards a single, distant point you can never actually see. Thus you never "see" the event horizon, and can't begin to estimate where it actually begins or ends, you just see that the entire universe seems to be rapidly expansing and moving away from you at ever increasing speed except for this one really weird region directly in front of you... And then tidal forces rip you to shreds.

I only saw the test on this once on vimeo. It was ALOT creepier than what they ended up going with, but I can see why they went with the other one with the overly-large black void. Black think "black hole" they want something BLACK, not a giant funhouse mirror with an invisible blender in the middle.

Anyway. Point is, there isn't really anything special about an "event horizon" that implies a small enough neutron star wouldn't also have one. Even if a dense object was still somewhat larger than it's Schwartzchild radius, the distortion of space would be so extreme that you STILL wouldn't really be able to see it; any visible light reflected from it would be scattered as hell and red-shifted WAY down into the radio/microwave spectrum  where there's be nothing there to "see" anyway, just a freakishly strong radio source in the middle of a what appears to a giant spherical lens that has no obvious boundary. More than a few physicists think this is probably what quasars are: massive ultra-dense objects of tens or hundreds of solar masses that, for whatever reason, didn't QUITE collapse below their event horizons but still have enough gravity to compress the entire spectrum into radio waves.