GW231123 is the most massive binary black hole merger detected by the LIGO-Virgo-KAGRA collaboration; its components lie in the pair-instability mass gap and exhibit extremely high dimensionless spin values. It has been shown that both black holes may have a primordial origin with smaller initial masses, and their current masses and, crucially, spins are naturally explained by accretion within the simplest models of primordial black holes. Interestingly, the parameter space required to reproduce the event rate of GW231123 lies at the boundary of the excluded zone from X-ray and relic observations, opening the possibility to either confirm or rule out this interpretation. The next observing run O5 is expected to detect around 20 such events, enabling a test of the mass–spin correlation, and next-generation detectors will be able to observe events at high redshifts as predicted by the scenario.
Detectors of gravitational waves caught the merger of two unusually heavy black holes — event GW231123. Their mass is too large to come from ordinary stars. Scientists believe they grew from tiny seeds that appeared right after the Big Bang. This idea of primordial black holes was proposed by Stephen Hawking.
The growth of such a hole is like a whirlpool in a sink: the more matter it sucks in, the more massive it becomes and the faster it spins. Over billions of years, dust and gas spun it up to enormous speeds, explaining both the mass and spin of GW231123.
🎯 Primordial black holes could have formed from random clumps of energy in the first second after the Big Bang.
🎬 In science fiction, tiny primordial black holes are sometimes depicted as invisible 'bullets' that can pass through planets and cause disasters.