Scientists just found a loophole that could let black holes split in two

A theoretical study published in Physical Review D proposes that black holes might split into two under extreme conditions, overturning the conventional understanding that they only merge.

The research, titled "When Black Holes Admit Pair-of-pants Topologies," examined the physical laws preventing black holes from dividing. Francesco Sannino, a professor of physics at University of Naples Federico II and the Quantum Field Theory Center at University of Southern Denmark, led the work alongside Giacomo Cacciapaglia from the French National Centre for Scientific Research, Manuel Del Piano, and Vania Vellucci.

Thermodynamics normally prevents a non-rotating black hole from splitting. Entropy, which describes the microscopic arrangements a system can have, decreases when a single black hole divides into two smaller ones. This thermodynamic unfavorability keeps black holes intact.

However, the team found that rapid rotation could open a narrow path around this restriction. A sufficiently fast spinning black hole might overcome the entropy barrier. Yet another obstacle remains. The two resulting black holes would need to separate far enough to avoid immediately merging again.

"When we include this requirement, the window largely closes again, except possibly for black holes rotating close to their maximum possible rate," Sannino said.

In theoretical models with extra spatial dimensions, black holes can become unstable and break apart. In some cases, splitting could even become thermodynamically favorable, particularly when one resulting black hole is much smaller than the other.

Researchers cannot yet calculate a single probability for black hole splitting. Sannino noted that the answer depends on how gravity behaves beyond Einstein's theory. Small primordial black holes may be more prone to splitting than larger astrophysical ones.

Gamma-ray telescopes such as Fermi-LAT might detect splitting indirectly by observing signals from tiny black-hole fragments formed during mergers. No confirmed observation of black hole splitting currently exists.