Given that our first direct detections that confirmed the existence of black holes only occurred in this century, one can forgive humanity for not knowing a few things about these mysterious cosmic objects.
We don’t even know everything we don’t know, a fact that has become evident in a new discovery. While doing equations for quantum gravity corrections for the entropy of a black hole, a couple of physicists found that black holes put pressure on the space around them.
Of course, there is not much pressure, but it is a fascinating finding consistent with Stephen Hawking’s prediction that black holes emit radiation and therefore not only have temperature, but slowly decrease over time, in the absence of accretion.
“Our finding that Schwarzschild black holes have pressure and temperature is even more exciting as it was a total surprise,” said physicist and astronomer Xavier Calmet of the University of Sussex in the UK.
“If we consider black holes only within general relativity, it can be shown that they have a singularity in their centers where the laws of physics as we know them must be decomposed.
“It is hoped that when quantum field theory is incorporated into general relativity, we can find a new description of black holes.”
When they made their discovery, Calmet and his University of Sussex colleague, physicist and astronomer Folkert Kuipers, were performing calculations using quantum field theory to try to investigate the event horizon of a black hole.
Specifically, they were trying to understand the fluctuations in the event horizon of a black hole that corrected its entropy, a measure of the progression of order to disorder.
As they performed these calculations, Calmet and Kuipers continued to cross an additional figure that appeared in their equations, but it took them a while to recognize what they were looking at: pressure.
“The moment the pine fell when we realized that the mysterious result of our equations told us that the black hole we were studying had a pressure (after months of fighting it) was stimulating,” Kuipers said.
It is unclear what causes the pressure and, according to team calculations, is very small. In addition, it is negative, expressed as -2E-46bar for a black hole the mass of the Sun, compared to the 1bar of the Earth at sea level.
That means exactly what it looks like: it means the black hole would shrink and not grow. This is consistent with Hawking’s prediction, although at this point it is impossible to determine the negative relationship of pressure to Hawking radiation, or even whether the two phenomena are related.
However, the finding could have interesting implications for our attempts to square general relativity (at the macro scale) with quantum mechanics (operating at extremely small scales).
Black holes are believed to be the key to this endeavor. The singularity of the black hole is mathematically described as a one-dimensional point of extremely high density, at which point general relativity decomposes, but the gravitational field around it can only be described relativistically.
Finding out how the two regimes fit could also help solve a very thorny black hole problem. According to general relativity, information that disappears beyond a black hole could disappear forever. Under quantum mechanics, it cannot be. This is the paradox of black hole information and mathematically exploring space-time around a black hole could help solve it.
“Our work is a step in that direction,” Calmet said, “and while the pressure exerted by the black hole we were studying is small, the fact that it is present opens up many new possibilities, covering the study of the ‘astrophysics, physics and quantum physics’.
The research has been published in Physical check D.