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The black holesCelestial bodies are so compressed that the intensity of their gravitational fields prevents any form of matter or radiation from escaping, astonishing scientists and amateurs. Among the many mysteries they perpetuate, the path of their death is one of the most intriguing. Stephen Hawking demonstrated the possibility of black holes evaporating and disappearing, but unfortunately contradicts general relativity: it is an information paradox. Recently, a team of researchers exploited a theory known as “Einstein-Delaton-Gauss-Bonnet gravity” to study the end states of black hole evaporation. Their discovery, which has not yet been confirmed, sheds new light on these celestial bodies.
A black hole is a celestial body whose gravity is so intense that it swallows everything beyond the “event horizon”, including light. The event horizon of a black hole marks the boundary beyond which nothing can appear. These celestial bodies are an essential part of the structure of the universe. The strong gravitational pull of black holes (or by singularity more precisely) is caused by matter being compressed into a small space. This can happen towards the end of a star’s life, making many black holes the result of the dying stars. By the way, there are black holes in the center of most galaxies, including our own. But we still don’t know exactly how these things die.
Stephen Hawking demonstrated the possibility of black hole evaporation, a phenomenon he named Hawking radiation. In other words, it is the radiation that any black hole would emit due to the laws of quantum mechanics, which causes it to evaporate with a loss of mass and angular momentum if the black hole is spinning and electrical charge if it is charged.
But according to general relativity, this phenomenon is impossible, because nothing that enters the event horizon of a black hole can leave it. However, this theory predicts the existence of points of infinite density where the laws of physics break down: singularities. This is what lies at the center of black holes, where all the matter in the star is concentrated. So what happens when a black hole evaporates? Scientists have used a certain theory to study these end states. Their results are available at arXiv, pending peer review.
A new theory to understand the death of black holes
Thus, the appearance of Hawking radiation created the information paradox of the black hole. In March 2022, scientists assumed that black holes would not forever swallow the information falling inside them: rather, they would affect their gravitational field.
Moreover, by studying the process of Hawking radiation, it will be possible to understand the physics of the singularity, which is likely to contain the information swallowed up by the black hole. As black holes evaporate, they get smaller and smaller and their event horizons approach central singularities. In the last moments of a black hole’s life, gravity becomes too strong and black holes become too small to be described and understood through the prism of current knowledge. So it becomes necessary to develop a better theory of gravity.
Sure, relativity and quantum mechanics don’t work well together, but using the different elements offered by these two theories is a possible way. There are many candidates for quantum gravity, starting with modified general relativity. Study researchers looked at the theory known as Einstein-Delaton-Gauss-Bonnet gravity.
The unexpected death of black holes
Unfortunately, the details of the team’s results are a bit blurry. This is because modified general relativity is not as well understood as classical general relativity, and solving equations depends on a lot of guesswork. However, researchers were able to characterize the death of a black hole in accordance with the nature and evolution of the latter.
You should know that a key feature of the Einstein-Delaton-Gauss-Bonnet theory of gravity is that black holes have a small mass, so the authors were able to study what happens when an evaporating black hole begins to reach a minimum mass.
Thus, on the one hand, the evaporation process can leave behind a residual “microscopic mass”, devoid of the event horizon. The authors believe that, in theory, it would then be possible to recover this “solid mass” that contains all the information that fell into the original black hole, thus solving the information paradox. On the other hand, a black hole can reach its minimum mass and give up its event horizon while retaining its singularity. These “naked singularities” seem forbidden in general relativity, but if they existed, they would serve as direct windows into the realm of quantum gravity.
Pending confirmation that Einstein-Delaton-Gauss-Bonnet gravity may represent a valid path to quantum gravity, results like those presented in this study will help physicists develop valid scenarios for how black holes might evolve.