For decades, we’ve known black holes can merge, growing ever larger. But could the opposite be true? New theoretical calculations suggest a mind-bending possibility: a single black hole splitting in two, a cosmic divorce that defies long-held rules.
The Universe’s Ultimate One-Way Street
Think
of a black hole and you likely picture an inescapable cosmic vacuum cleaner. It's a region of spacetime where gravity is so intense that nothing, not even light, can escape once it crosses a boundary called the event horizon. This understanding, built on Einstein's theory of general relativity, has painted a clear picture of black hole behaviour. We have detected the gravitational waves from black holes colliding and merging into one larger entity, an event now routinely observed by detectors like LIGO. This process follows a fundamental rule of physics related to entropy—a measure of disorder. According to a theorem proposed by Stephen Hawking, the total surface area of a black hole's event horizon, which is tied to its entropy, cannot decrease. Splitting one black hole into two smaller ones would violate this rule, as the combined area of the two new horizons would be less than the original. This is why, for decades, black hole fission was considered impossible.
Finding a Loophole in the Laws of Physics
A new theoretical study, published in the journal Physical Review D, proposes a fascinating exception to this rule. An international team of physicists explored whether extreme conditions could allow a black hole to bypass these limitations. Their calculations suggest that if a black hole is rotating at, or very near, the maximum possible speed allowed by physics, a split might just be possible. For a non-rotating black hole, a split is thermodynamically forbidden because it would decrease its entropy. But an extremely fast-spinning black hole has a smaller initial surface area for its mass. The new theory suggests it could convert its immense rotational energy into the orbital motion of two new, smaller black holes, allowing their combined surface area to be greater than the original, thus satisfying the laws of thermodynamics.
The ‘Pair-of-Pants’ Split
The researchers have nicknamed this hypothetical process a 'pair-of-pants topology'. Imagine the event horizon of the original black hole tracing a path through spacetime. In a split, this path would look like a single tube branching into two separate 'legs', like a pair of trousers. Each leg would represent the event horizon of a new, smaller black hole. However, the conditions for this to occur are incredibly restrictive. Not only must the original black hole be spinning at its absolute limit, but the two resulting black holes must also fly apart fast enough to escape each other’s gravitational pull and avoid immediately merging back into one. When this requirement is factored in, the window of possibility narrows dramatically, making it an exceptionally rare event, even in theory.
Why This Theory Matters
While no one has ever observed a black hole splitting, these calculations are more than just a fascinating thought experiment. They push the boundaries of our understanding of gravity and general relativity. If such an event could be proven, it would reveal how physics operates under the most extreme conditions imaginable and could point to where Einstein's theories might need revision. Some researchers suggest that these splits might be more likely for smaller, 'primordial' black holes, which are hypothesised to have formed in the early universe. The search for evidence is already being contemplated. Scientists believe that if a split were to occur, it might release detectable signals, such as powerful bursts of gamma-rays. Telescopes like NASA's Fermi-LAT could potentially hunt for these faint cosmic flashes, providing the first clues that this process is more than just a theory.
