However, these properties will not last long, and the black hole will become "bare (hairless)" and become indistinguishable from other black holes of the same kind. Physicist and research author Lior Burko said: this is an interesting discovery because it is a short-lived behavior. The metaphor of black hole hair comes from the mathematical calculations made by physicists Jacob Bekenstein and John Wheeler in 1960s and early 1970s.
According to Einstein's general theory of relativity, black holes can only be described by three observable parameters: ① mass, ② angular momentum and ③ charge. Everything else, all other information, is trapped by the gravity of the black hole, so it is impossible to be observed. Assuming that two black holes meet all three values, it is impossible to distinguish them.
The visualization of supercomputer simulation shows the behavior of positrons near the event horizon of rotating black holes. Photo: Kyle Pavley et al./Berkeley Lab
Since then, theorists have been looking for something that can distinguish black holes. If scientists can find something, it may open up new discoveries about the origin of specific black holes. For example, although many black holes are considered to be remnants of collapsed stars, some black holes may have formed after the Big Bang and merged from unusually dense areas in the earliest cosmic structure.
If one of the primitive black holes has the same mass, angular momentum and charge, they will be indistinguishable from stellar black holes. A group of researchers led by Dejan Gajic, a physicist at Cambridge University, found that extreme black holes (black holes with the highest possible charge) do have unique properties and can distinguish black holes. These properties involve the measurable changes of the event horizon (the point where the gravity is so strong that light cannot escape) and the cauchy horizon (the point where the causal relationship between the past and the future collapses due to the time bending effect of the strong gravitational field) of the black hole. Burko and his colleagues began to be interested in whether black holes have unique properties.
(The picture shows Boko Park) The event horizon telescope is a planetary array composed of eight ground radio telescopes through international cooperation. It captured this image of the supermassive black hole and its shadow in the center of M87 galaxy. Photo: EHT collaboration
These black holes are almost extreme, but not complete. And two kinds of black holes are calculated. The first one is the almost extreme Reissner-Nordstr? M black hole, which is a kind of black hole with almost the largest possible charge but does not rotate. The second is the almost extreme kerr black holes, a black hole with almost maximum spin but no charge. Among these two extreme black holes, scientists have found evidence that black holes are hairy. Its findings were published in the journal Physical Review Research. When a simulated black hole is formed for the first time, the unique properties of the black hole close to the extreme can be measured, but it will decrease with the quadratic function of time as time goes on.
This means that these values will shrink rapidly at first, and then continue to shrink at a slower rate over time. (The research team did not calculate the speed of this process in real time, which depends on the mass, spin and charge of a given black hole. )。 In a very short time (an almost extreme black hole) behaves like a black hole with hair, like a black hole with the largest rotation. But after a while, the black hole began to shed these hairs and eventually became a "bald" hairless black hole. Although all these calculations are theoretical at present, observations in the real world may match or contradict these findings, but it is hopeful.