Black Holes

Much of what we have done above is most relavant to Black Holes which are very compact objects. It is possible that some black holes were formed in the Big Bang but we have no evidence of this. We observe Black Holes that have been formed from the gravitational collapse of large stars. We observe huge Black Holes at the center of most galaxies including ours. We observe supernovae that occur when stars collapse down to neutron stars or to black holes.

It has been predicted by Hawking that the strong gravitatonal field of Black holes causes radiation to be emitted outside the Schwarzschild radius that escapes to infinity. This causes black holes to evaporate, if they are not acreting matter. Very light Black Holes can evaporate quickly. Large Black Holes will take a very long time, particularly since more and more matter is falling into them.

But this evaporation has implications. The Black Hole evaporates in a finite amount of time as viewed from large $r$. On the other hand it takes an infinite amount of time for light emitted at $r_s$ to emerge. So it must be that, as observed from large $r$, the Black Hole collapses down to nearly the Schwarzschild radius, then slows to zero, and emits radiation, eventually evaporating. So as seen from the outside, the Black Hole never collapes to a point. It actually maintains all its information in a thin layer near $r=r_s$.

On the other hand, there may be fully collapsed pointlike black holes created in the big bang.

The quantum theory of gravity may have some impact on these speculations, including the Hawking radiation.