At first, the release of black hole energy is very small, however, with the contraction of black hole, the speed of energy release will accelerate. Until the last moment of a black hole's life, it will release enormous energy and then disappear completely. Later, the process of this black hole releasing energy is called Hawking radiation, which is the result of quantum field theory.
Hawking imagined drawing a line through time in the space before the birth of a black hole, and the quantum field vibrating along this line extended from before the existence of the black hole to the future after the existence of the black hole. Before the black hole was born, everything was normal, and the quantum field vibrated freely, which could cancel each other out. However, the appearance of black holes changes the curvature of space. Hawking realized that not all the * * * vibrations were cancelled after the black hole appeared. Outside the event horizon far away from the black hole, he found the * * * vibration that was completely matched with the thermal radiation flying into space.
However, as Hawking predicted, it is very difficult to prove Hawking radiation because it is very weak compared with cosmic background radiation. Despite some objections, the mathematical principle behind Hawking radiation is reasonable, and scientists have taken measures to prove it. In the laboratory of Israel Institute of Technology, researchers studying Hawking radiation came up with a method to overcome the difficulty of measuring real black holes.
They do this by creating a simulator-acoustic black holes, which can imitate the characteristics of real black holes. The speed of sound is much slower than the speed of light, so it is much easier to create a medium that travels faster than the speed of sound. When the medium is moving, any sound wave propagating in the same direction can't completely escape from it, thus producing the horizon of the sound wave black hole. Interestingly, Hawking's mathematical method is suitable for acoustic black holes, just as it is suitable for gravitational black holes, so Hawking radiation should be detected in acoustic black holes.
In this experiment, the medium is a gas composed of 8000 atoms, which are cooled to near absolute zero by laser to form Bose-Einstein condensate. Then, the second laser beam drives it to start flowing, and the flow speed exceeds the local sound speed. The researchers' goal is to find quantum sound wave pairs spontaneously formed outside the horizon. After discovering these quantum acoustic pairs, it is necessary to confirm whether they are related to experiments or just caused by external disturbances.
In the continuous experiment of 124 days, the researchers repeated the experiment 97000 times. They tested several examples of Hawking radiation and found that it was consistent with Hawking's prediction of the possible behavior of radiation. Although this does not prove that Hawking radiation really exists in real black holes, the fact that Hawking's mathematical method works in the simulation of acoustic black holes strongly suggests the possibility of Hawking radiation.