Previously, it was believed that the black holes are inert, the final stages of a dying star. Then, in 1974, Professor Stephen Hawking discovered that black holes emit thermal radiation.

Now, scientists at the University of Sussex have discovered that black holes are even more complex thermodynamic systems, with a temperature and a pressure. Scientists reached this conclusion after finding out that black holes exert pressure on their environment.

Scientists were puzzled by an extra figure appearing in equations that they were running on quantum gravitational corrections to the entropy of a black hole.

During the discussion, they realized that what they were seeing was behaving as a pressure dawned. They confirmed their exciting finding that quantum gravity could lead to pressure in black holes following further calculations.

Xavier Calmet, Professor of Physics at the University of Sussex, said: *“Our finding that Schwarzschild black holes have pressure, as well as a temperature, is even more exciting given that it was a total surprise. I’m delighted that the research that we are undertaking at the University of Sussex into quantum gravity has furthered the scientific communities’ wider understanding of the nature of black holes.”*

*“Hawking’s landmark intuition that black holes are not black but have a radiation spectrum that is very similar to that of a black body makes black holes an ideal laboratory to investigate the interplay between quantum mechanics, gravity and thermodynamics.”*

*“If you consider black holes within only general relativity, one can show that they have a singularity in their centers where the laws of physics as we know them must breakdown. It is hoped that when quantum field theory is incorporated into general relativity, we might be able to find a new description of black holes.”*

*“Our work is a step in this direction, and although the pressure exerted by the black hole that we were studying is tiny, the fact that it is present opens up multiple new possibilities, spanning the study of astrophysics, particle physics, and quantum physics.”*

*Folkert Kuipers, a doctoral researcher in the School of Mathematical and Physical Science at the University of Sussex, said: “It is exciting to work on a discovery that furthers our understanding of black holes – especially as a research student.”*

*“The pin-drop moment when we realized that the mystery result in our equations was telling us that the black hole we were studying had a pressure – after months of grappling with it – was exhilarating.”*

*“Our result is a consequence of the cutting-edge research that we are undertaking into quantum physics at the University of Sussex, and it shines a new light on the quantum nature of black holes.”*

##### Journal Reference:

- Xavier Calmet and Folkert Kuipers. Quantum gravitational corrections to the entropy of a Schwarzschild black hole. DOI: 10.1103/PhysRevD.104.066012