Can a black hole split in two? While traditionally considered impossible, a study published in Physical Review D suggests that black holes rotating near their maximum speed could theoretically fragment. This process, termed “pair-of-pants topology,” would require specific conditions to overcome thermodynamic laws and gravitational attraction.
Why do the laws of physics normally prevent black holes from splitting?
The primary obstacle is entropy, which measures the microscopic arrangements of a physical system. For a non-rotating black hole, entropy is proportional to the surface area of its event horizon. According to a rule formulated by Stephen Hawking in 1971, the surface area of a black hole’s event horizon cannot shrink.
ZME Science reports that if a stationary black hole were to divide into two smaller pieces, the combined surface area of those fragments would be smaller than the original. Because the universe requires total entropy to increase or remain constant, such fragmentation is thermodynamically unfavorable.
Did you know? Researchers analyzing the GW250114 gravitational-wave collision confirmed Hawking’s area theorem, observing two colliding black holes form a merged horizon larger than the sum of their individual parts, as reported by ZME Science.
How does rotation create a loophole for fragmentation?
A study involving Francesco Sannino of the University of Naples Federico II and the Quantum Field Theory Center suggests that rapid rotation changes the relationship between mass, angular momentum, and entropy. The team’s calculations show a spinning black hole possesses lower entropy than a non-rotating one of the same mass.
If a rapidly spinning black hole splits, it could convert its internal spin into the orbital angular momentum of two receding fragments. This conversion allows the combined entropy of the two smaller black holes to approach or exceed that of the original, potentially bypassing the thermodynamic barrier.
What is the “pair-of-pants topology” and how does it work?
The term describes the visual shape the event horizon would take during a split. ZME Science explains that if a spacetime diagram is viewed with time flowing vertically, a single black hole looks like a solid tube. If that boundary pinches and divides, it branches into two separate tubes.
This branching effect resembles the waistband of a pair of trousers splitting into two legs. Sannino describes this as the event horizon forming a trouser-like shape as the fragmentation proceeds.
Why is a split still unlikely to happen?
Solving the entropy problem is only the first step. The two resulting black holes must also possess enough outward momentum and energy to escape one another’s gravity. Sannino stated that when this requirement is included, the window for splitting “largely closes again,” remaining possible only for black holes rotating close to their maximum possible rate.
The researchers also examined alternative theories of gravity and extra spatial dimensions. In higher-dimensional models, structures like “black strings” can become unstable and split, particularly when the resulting fragments are very unequal in size.
How could scientists detect a black hole split in the future?
While no such event has been witnessed, Sannino suggests that small primordial black holes are more likely to split than larger astrophysical ones. The team believes indirect detection may be possible using gamma-ray telescopes.
Specifically, the Fermi-LAT telescope could be used to search for signals from tiny black-hole fragments that might form during mergers.
Black Hole Fragmentation Comparison
| Feature | Non-Rotating Black Hole | Rapidly Rotating Black Hole |
|---|---|---|
| Entropy Level | Higher (relative to mass) | Lower (relative to mass) |
| Splitting Probability | Thermodynamically unlikely | Theoretically possible |
| Horizon Shape | Stable sphere/tube | Potential “pair-of-pants” |
Common Questions About Black Hole Splitting
Does this mean Einstein’s theory of general relativity is wrong?
Not necessarily. The study explores how gravity behaves beyond Einstein’s theory to quantify the probability of splits. Sannino notes that the possibility depends on these broader gravitational behaviors.
Which black holes are most likely to split?
Small primordial black holes are considered more prone to fragmentation than the massive astrophysical black holes found at the centers of galaxies.
Has any telescope ever seen a black hole divide?
No. This research remains theoretical, and the “pair-of-pants” event has not been observed by any current astronomical instrument.
Researchers continue to work on quantifying the probability of these events, focusing on the interplay between mass, angular momentum, and the behavior of gravity in higher dimensions.
Worth a look