Scientists find loophole that lets black holes split apart

When two black holes collide, they can merge into one enormous black hole. But what if one black hole could do the opposite and split into two? A new theoretical study suggests that this strange possibility isn't completely forbidden by physics. Under extraordinarily specific conditions, a black hole spinning close to its maximum possible speed could potentially divide into two smaller black holes.

The research, published in Physical Review D under the title "When Black Holes Admit Pair-of-pants Topologies," examines the physical laws that normally keep black holes intact and what might happen when those rules are pushed to their limits. According to Francesco Sannino, a co-author of the study and professor of physics at the University of Naples Federico II and the University of Southern Denmark, the team wanted to understand which laws prevent black holes from splitting and whether certain circumstances could get around those restrictions.

Why black holes don't normally split

The biggest obstacle is a concept called entropy. In simple terms, entropy describes the number of possible microscopic arrangements within a system. Black holes have entropy too, and it plays an important role in determining how they can change.

For a non-rotating black hole, splitting into two smaller black holes would reduce the total entropy. That makes the process thermodynamically unfavorable. In other words, the physics doesn't naturally allow a black hole to break itself into smaller pieces.

This is one reason black holes are generally expected to merge rather than fragment. But the researchers found that rotation could complicate that rule.

Spinning black holes may have a loophole

According to the team's calculations, a black hole rotating at an exceptionally high speed could potentially get around the usual thermodynamic restriction. There is a catch, though. Producing two black holes is not enough. They would also need to move far enough apart to avoid immediately falling back together and merging again.

Sannino explains that once the researchers account for this separation requirement, the window for a split becomes extremely narrow. It may only remain open for black holes spinning close to their maximum possible rate.

Extra dimensions could make splitting easier

The researchers also explored more exotic possibilities involving theories that propose additional dimensions beyond the three dimensions of space we experience. Some theoretical models already contain black-hole-like objects that can become unstable and begin fragmenting.

Under certain conditions, splitting could even become thermodynamically favorable, particularly when one of the resulting black holes is much smaller than the other. That doesn't mean the process would automatically happen. The researchers still need to establish what conditions would make fragmentation possible.

Catch a black hole splitting?

The researchers say they cannot yet assign a probability to black holes splitting. According to them, the answer depends partly on how gravity behaves beyond Einstein's theory of general relativity. They suspect that small primordial black holes, which may have formed in the early universe, could be more prone to splitting than the much larger black holes astronomers observe today.

There may also be a way to look for indirect evidence. Sannino points to gamma-ray observatories such as NASA's Fermi Large Area Telescope (Fermi-LAT), which could search for signals from tiny black-hole fragments potentially produced during mergers.

For now, nobody has confirmed that a black hole has ever split apart. The study is a theoretical exploration, not an astronomical discovery. Still, it sure challenges the usual picture of black holes as objects that only grow by swallowing matter or merging with other black holes.

Source: ScienceDaily

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