Black holes are best known for merging, but new theoretical research suggests that, under extraordinarily extreme conditions, a rapidly spinning black hole might split into two smaller ones. The process is normally blocked by thermodynamics and by the risk that the two resulting black holes would quickly merge again, but the researchers say a narrow possibility may remain for objects rotating near their maximum possible speed or existing in theories with additional dimensions.
Why black holes normally do not split
The study, published in Physical Review D under the title “When black holes admit pant topology,” examines the physical laws that normally keep black holes intact and the circumstances that might allow them to fragment.
“In our study, we investigate what physical laws normally prevent a black hole from splitting into two. We also investigate whether certain circumstances can cause splitting to occur,” says study co-author Francesco Sannino, professor of physics at Italy’s Federico II University of Naples and the Center for Quantum Field Theory at the University of Southern Denmark.
The research team also included Giacomo Cacciapaglia, a researcher at France’s National Center for Scientific Research (CNRS) and the Institute for Physics and Autoenergetics, a joint research institute between CNRS and Sorbonne University in Paris. Manuel Del Piano and Vania Vellucci, both from the Center for Quantum Field Theory at the University of Southern Denmark, were additional contributors.
One of the main obstacles to black hole splitting comes from thermodynamics, the branch of physics that describes how energy behaves and how physical systems change.
Entropy is central to the problem. It measures the number of microscopic configurations a system can have while still appearing the same to the outside world. Black holes possess entropy, and that property places important limits on what can happen to them.
For a non-rotating black hole, splitting into two smaller black holes would reduce the total entropy. Because such a decrease is thermodynamically unfavorable, it helps explain why black holes normally do not divide.
How extreme rotation could change the picture
The researchers’ calculations suggest that very rapid rotation could create a narrow opening in the physical constraints that usually prevent black hole splitting. In principle, a black hole spinning fast enough could overcome the usual thermodynamic barrier.
Even then, another major obstacle would remain: the two resulting black holes would need to move far enough apart to avoid quickly merging again.
“But the two resulting black holes must be able to separate, rather than quickly coming back together. Including this requirement almost closes the window again, except for black holes that rotate at speeds close to their maximum possible speed,” Sannino says.
The study’s title refers to the shape traced by a black hole’s boundary through space and time if such a breakup occurred. This boundary, known as the horizon, would begin as a single structure and then divide into two branches.
Viewed over time, the resulting shape resembles a pair of trousers, with one upper section leading to two “legs.” This is the origin of the term “pants topology.”
Additional dimensions could provide another route
The researchers also examined more unusual scenarios based on theories in which space has additional dimensions beyond the three experienced in everyday life.
Some theoretical models already contain black hole-like objects that can become unstable and begin to break apart. These possibilities suggest that the familiar rules governing black holes may work differently under less conventional conditions.
In some cases, splitting could even be thermodynamically favorable, particularly when one of the resulting black holes is much smaller than the other. However, a process that is allowed or favored by thermodynamics is not necessarily guaranteed to occur. Researchers must still determine whether the fragmentation is physically possible and what conditions would enable it.
Could astronomers detect black hole fragmentation?
Scientists are still working to determine how likely such events might be. The answer could depend on aspects of gravity that extend beyond Einstein’s theory of general relativity, making the problem especially difficult.
“We still cannot give a single probability that a black hole will split up. It depends on how gravity behaves beyond Einstein’s theory, and we are working to quantify this,” Sannino says.
He adds that small primordial black holes could behave differently from much larger astrophysical black holes and may be more prone to fragmentation. The researchers suggest that fragmentation might be detectable indirectly: gamma-ray telescopes such as Fermi LAT could search for signals from small black hole fragments produced during mergers.
There are currently no confirmed observations of black hole fragmentation. Detecting signals from possible small fragments would nevertheless provide a way to investigate the idea and could offer clues about how gravity behaves under the universe’s most extreme conditions.
Sannino is director of the Quantum Field Theory Center (ℏQTC) at the Faculty of Mathematics and Computer Science (IMADA) at the University of Southern Denmark. He is also affiliated with the Danish Institute for Advanced Study and the Department of Physics “Ettore Pancini” at the University of Naples Federico II. In addition, he is a visiting professor at Durham University.
Source: www.sciencedaily.com
