Wednesday, September 24, 2014

About Black Holes

Long time readers, if any, may recall that I'm fond of the semi-crackpot idea that black holes don't really exist. Two new papers by Mersini-Houghton and Pfeiffer make just just such a claim: I and II.

The abstract of the latter:

A star collapsing gravitationally into a black hole emits a flux of radiation, knowns (sic) as Hawking radiation. When the initial state of a quantum field on the background of the star, is placed in the Unruh vacuum in the far past, then Hawking radiation corresponds to a flux of positive energy radiation travelling outwards to future infinity. The evaporation of the collapsing star can be equivalently described as a negative energy flux of radiation travelling radially inwards towards the center of the star. Here, we are interested in the evolution of the star during its collapse. Thus we include the backreaction of the negative energy Hawking flux in the interior geometry of the collapsing star and solve the full 4-dimensional Einstein and hydrodynamical equations numerically. We find that Hawking radiation emitted just before the star passes through its Schwarzschild radius slows down the collapse of the star and substantially reduces its mass thus the star bounces before reaching the horizon. The area radius starts increasing after the bounce. Beyond this point our program breaks down due to shell crossing. We find that the star stops collapsing at a finite radius larger than its horizon, turns around and its core explodes. This study provides a more realistic investigation of the backreaction of Hawking radiation on the collapsing star, that was first presented in [1]

The authors don't comment, so far as I can tell, on the implications for all those black hole like objects that occupy our universe. Perhaps they are "frozen stars" in the sense that some early investigators understood black holes. Even if the stars involved never collapse to actual black holes, the intense gravity causes time to slow down so much that it takes zillions of years for the news to reach us.