Two physicists at the University of Sussex have made a startling discovery about black holes: they exert a pressure on their environment. Previously, black holes were believed to have a temperature caused by emitting radiation, but were thought to be inert when it came to pressure. Even earlier, black holes were considered fully inert with no temperature, but the late Stephen Hawking changed that in the 1970’s with his discovery of Hawking radiation, a small amount of thermal radiation released near the black hole’s event horizon, a kind of outer edge. The momentous discovery of temperature in black holes sets the stage for this new finding, that they also have a pressure.
The discovery was made by University of Sussex Professor Xavier Calmet, of the Department of Physics and Astronomy, and doctoral researcher Folkert Kuipers, of the school of Mathematical and Physical Science. The physicists were studying the entropy of a black hole and found a confusing figure when making “quantum gravitational corrections.” They realized on Christmas of 2020 that the extra figure they found was acting like, and in fact was, a pressure coming from the black hole. While the pressure is extremely small in magnitude, the discovery that “quantum gravity can lead to a pressure in black holes” is anything but small in its magnitude of impact to the fields of astrophysics and quantum physics.
Black holes are intriguing points of study in the varied world of physics because their center, the singularity, represents a point where a lot of our current understanding of physics breaks down. This offers an opportunity to learn about the edges of the field, a notable instance of which is quantum gravity. Gravity is a force which has yet to be unified with the rest of physics. Whereas other fundamental forces, like the electromagnetic force or the weak nuclear force, can be explained in our Standard Model of quantum physics, gravity still stands in relative separation. The study of quantum gravity, chiefly in relation to black holes, is an attempt to figure out the interplay between gravity and quantum physics well enough to unite them under a single theory or frame of understanding.
This discovery will help to move forward the physical understanding of black holes and quantum gravity. As Kuipers notes in a university press release, “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.”
Article Image Source: Center for Astrophysics | Harvard & Smithsonian