NU Professor Daniele Malafarina from the School of Sciences and Humanities (SSH) and researchers from the Observatory of the National Institute of Astrophysics (INAF) in Catania (Italy) study the problem of gravitational collapse and the formation of non-singular black holes. They developed their new theory based on the ideas of scientists Markov and Mukhanov. Their little-known paper was brought to the attention of Prof. Bonanno of the INAF observatory in Catania.
“Our non-singular black hole is obtained as the end state of collapse of ordinary matter in the so-called Asymptotically Safe theory of gravity. In the proposed model, instead of reaching the center in a finite time, matter takes an infinite amount of time to collapse thus avoiding the formation of the singularity, while still forming a black hole horizon, which is the region from which not even light can escape,” explained professor Malafarina.
From Einstein’s theory of general relativity, it is known that black holes are born from the collapse of massive stars. Because of collapse, a ‘singularity’ forms at the center of the black hole. The black hole singularity is a region of zero volume and infinite density containing the black hole mass. However, the existence of singularities is a problem for the theory. Singularities are not expected to occur in the real universe, but some theorems show they are inevitable in general relativity.
“There are many research groups that have been working for a long time trying to understand how to obtain black holes without singularities in Einstein’s theory and in alternative theories. Other models of non-singular black holes are obtained not as the end result of the collapse or have other undesirable features, such as they require negative densities or other exotic matter, and in some instances, they don’t even form black holes at all, for example bouncing and turning into white holes instead. Personally, I have been interested in the problem for many years as I believe that the resolution of singularities may be a step towards a new and better theory of gravity,” noted Professor Malafarina.
The first direct image of a black hole, whose existence was predicted as an exact mathematical solution to Einstein’s equations, was obtained in 2019 by the Event Horizon Telescope (EHT). This black hole sits at the center of the massive galaxy Messier 87, 55 million light-years away from Earth, and is estimated to weigh 5 billion times the mass of the Sun. The Milky Way also contains one very massive black hole at its center (which was imaged by the EHT in 2022) and, by some estimates, it is expected to contain more than 100 million smaller black holes, each as massive as a few times the Sun’s mass.
Image: The first image of the black hole captured by the Event Horizon Telescope (EHT).
“The most significant aspect of our proposal is that it achieves the goal without any of the existing proposals’ shortcomings, thus making the model more appealing from a physical perspective. I do not believe that ours is the final word on black hole formation, but hopefully, it constitutes an interesting and useful step forward. The results hint at how gravity may behave in the extreme conditions that occur when a black hole forms, and this will hopefully help us understand what features a new theory of gravity must possess,” said the scientist.
The scientists’ collaborative work has recently been published by the American Physical Society’s (APS) flagship journal, Physical Review Letters (PRL), with an impact factor of 8.6 and ranking in the top 6% of the General Physics and Astronomy category in Scopus. An article published in PRL usually indicates that its results deserve the attention of a broad audience of physicists.
