Could a Spinning Black Hole Split in Two? Physicists Run the Numbers

Black holes are known for merging, not breaking apart. But a team of physicists has calculated that, under the right conditions, a black hole could split into two, according to Universe Today. The idea is purely theoretical, and no one has observed such an event.

The researchers include Francesco Sannino of the University of Naples Federico II in Italy and the Quantum Field Theory Center at the University of Southern Denmark, along with Giacomo Cacciapaglia, Manuel Del Piano and Vania Vellucci. They studied possible mechanisms for black hole fragmentation and worked out what would have to happen for a split to occur.

Why a split is so hard

Black hole collisions are common in cosmic history and produce gravitational waves. Gravity near a black hole is so strong that it is hard to imagine any force tearing one apart, which is what made the question an unusual one for the team to take on.

The main obstacle is entropy, a measure of how many different microscopic arrangements a physical system can have while looking the same from the outside. For an ordinary black hole that is not rotating, splitting it into two pieces would lower its entropy. That makes the process thermodynamically unlikely, Universe Today explained.

What changes if the black hole spins

Rotation changes the picture. According to the team, spin alters the relationship between a black hole’s mass, its angular momentum and its entropy, and that shift could make fragmentation possible. A very rapidly spinning black hole could, in principle, break into two pieces.

There is a second hurdle. The two new black holes must be able to move apart rather than fall straight back together. Sannino said that once this requirement is included, the window for splitting largely closes again, except possibly for black holes rotating close to their maximum possible rate. Universe Today reports that both of the resulting black holes would also need to keep spinning at or near that maximum.

If a split did happen, the black hole’s event horizon would take on a trouser-like shape as it divided, with two legs joining a single body. The researchers call this a “pair-of-pants topology.” The two resulting black holes would then drift apart, keeping the momentum and speed of the original.

Which black holes might be candidates

Sannino said the team cannot yet give a single probability that a black hole will split. He said it depends on how gravity behaves beyond Einstein’s theory, and the researchers are working to quantify that. He added that small primordial black holes should be more prone to splitting than much larger astrophysical black holes.

Universe Today noted that the black hole at the center of the galaxy M87 has a measured spin, so in theory it could break apart if conditions were right. The outlet also said such events seem unlikely to have happened, though the researchers do not rule out that they have occurred in specific cases.

Why it matters

This research does not change anything in daily life, and it does not suggest that any black hole near us is about to divide. Its value is in testing the limits of what physics allows. The result also ties the question to an open one: how gravity works beyond Einstein’s theory. The calculation shows that the answer would affect whether black holes can split at all.

The work is theoretical, and the authors say a single probability cannot yet be given. It remains a set of calculations rather than an observed phenomenon.

How a split could be detected

Sannino said a split might be detected indirectly. Gamma-ray telescopes such as Fermi-LAT can search for signals from tiny black-hole fragments that might form during mergers. If such signals turned up, they could point to fragmentation, though no such detection has been reported.

Around Prague, based on reporting by Universe Today