(ORDO NEWS) — Black holes are regions in space characterized by gravitational fields of such intensity that neither matter nor radiation can escape from them.
They are solutions of Einstein’s field equations, in the center of which there is a point with unphysically infinite density.
According to the classical theory of general relativity, all the matter that went into the formation of a black hole ends up in its center. This particular prediction is known as the “singularity problem”.
In one of his fundamental works, Stephen Hawking showed that black holes radiate energy and that they slowly disappear.
However, his work suggests that the radiation emitted by black holes does not contain all the information about the matter that went into their formation. In astrophysics, this is called the “information loss problem”.
Researchers at the University of New Brunswick in Canada have recently developed a theoretical model that effectively addresses both the singularity and information loss problems, and sheds more light on how matter collapses to form black holes.
The model they developed, presented in an article published in the journal Physical Review Letters, offers an alternative view of the formation and evolution of black holes compared to classical theories.
“The question of the fate of a black hole and what happens to the matter (or information) that formed it has been an open problem for fifty years,” said Vikar Husain Jarod George Kelly, Robert Santacruz and Edward Wilson-Ewing, scientists who conducted study.
“It is widely believed that a theory is needed to solve this problem. We know a lot about how collapsing matter forms black holes in general relativity, but the question of how collapse occurs in quantum gravity also remains an open problem.”
The main goal of the recent work of Husain and his colleagues was to create a model that exactly solves the problem of singularity and gravitational collapse at the same time.
To do this, they used the loop quantum gravity construct to incorporate the fundamental discreteness of space into the classical equations describing gravitational collapse.
“We studied the problem using simple dusty matter, which does not exert pressure because it is the simplest type of matter; its movement is described by a controlled equation that can be solved on a laptop,” Husain explained.
“This equation is a modified version of the classical Einstein equations that takes into account the fundamental discreteness of space at the microscopic level.”
The numerical method that the researchers used in their study was developed by Sergei K. Godunov, a well-known Russian scientist who conducted theoretical studies focused on fluid flow problems.
Remarkably, this method can work with the formation of a shock wave, a physical phenomenon that occurs when an object moves at supersonic speed and presses on the surrounding air (for example, when a jet stream breaks the sound barrier).
“We have followed the evolution of a cloud of collapsing dust particles to the formation of a black hole,” say Husain, Kelly, Santacruz and Wilson-Ewing. “The numerical method allowed us to trace the evolution of matter even inside the region of a black hole in the direction of the point where the singularity would be in the classical solution.”
The quantum gravity-corrected equation presented by Husain and colleagues solves the singularity problem more dynamically than classical models. More specifically, it suggests that matter falls into the center of a black hole, reaches a high but finite density, and then bounces back, forming a shock wave.
“The effects of quantum gravity are important to the shock wave and allow it to move outward inside the black hole, which is not possible using classical equations,” the researchers say. “At the same time, the curvature of space-time becomes large, but never diverges (as it happens in the classical theory).”
Using a numerical tool introduced by Godunov, the researchers were also able to calculate the lifetime of a black hole – from its formation to its disappearance, when the shock wave leaves its horizon and the horizons begin to disappear.
Interestingly, the black hole lifetime they calculated is much shorter than the evaporation time predicted by Hawking. This suggests that their model can help solve the problem of information loss, but more research is needed to confirm this.
In addition, the equation presented by Khusain and colleagues introduces the production of shock waves during the development of black holes. Thus, in the future, this may prompt astronomers to evaluate the possibility of detecting shock waves emanating from black holes.
“If this turns out to be possible, our results may provide a ready-made explanation; but this, too, requires further careful study,” the researchers added.
“In our next studies, we would like to try to establish whether the problem of information loss has indeed been solved, to study other types of matter that exert pressure, and other types of clouds of matter, to see if our result for shock waves remains qualitatively unchanged.
If this turns out to be the case, then shock waves could become a universal signature marking the death of a black hole.”
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