The black holes that produced the first detected gravitational waves may have exotic origins in the early universe.
When the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, glimpsed gravitational waves from two merging black holes, scientists were surprised at how large the black holes were — about 30 times the mass of the sun (SN: 3/5/16, p. 6). Inspired by this unusual finding, two papers published in Physical Review Letters propose that the hefty black holes were born in the universe’s infancy.
Unlike run-of-the-mill black holes that form from collapsing stars, such primordial black holes could have formed when dense regions of the very early universe collapsed under their own gravity, some theories suggest. If they exist, primordial black holes could also solve another puzzle: the identity of dark matter, the unknown source of mass in the universe that holds galaxies and galaxy clusters together. Primordial black holes could make up the universe’s missing mass, an idea that counters the more popular theory that dark matter is made up of undetected particles.
A Japanese team of astrophysicists reported August 2 that LIGO’s black holes may be primordial, and that, if so, they could make up some portion of the universe’s dark matter. Johns Hopkins University scientists reported May 19 that LIGO’s estimated rate of black hole mergers matches with that expected from primordial black hole dark matter.
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