After scientists announced they detected gravitational waves using both of the twin Laser Interferometer Gravitational Wave Observatory (LIGO) detectors back in February, physicists pointed to the merger of two astrophysical black holes as the origins of the ripples in space-time. Now, a new study suggests that these black holes might have been some of the first to form in the universe and suggest that dark matter could be made of black holes.
The primordial black holes in question would have been created following the Big Bang. When sound waves were shot through the hot plasma ball that spanned the universe, areas of high wave density likely collapsed to form them.
The team claims that if these black holes are present today in large enough numbers, they could make up dark matter, the elusive substance that makes up around 85 percent of the mass in the universe. Despite this large size, dark matter shows no signs of existence barring its effects on gravity, which means, so far, no conclusive evidence of its existence is known.
Researcher Simon Bird and his team believe that the gravitational waves detected by LIGO might stem from a pair or primordial black holes as opposed to astrophysical black holes, which are created from collapsing stars.
Bird believes the mass of LIGO's black holes suggests his theory is correct, as each is around 30 times the mass of the sun. Although primordial black holes can come in all kinds of masses, previous research suggests they can only exist within certain thresholds.
"There's actually a window where they're allowed, and it just happens to go straight through where the LIGO detection was," Bird said.
Following observations of its mass, the team assumed that all dark matter is composed of primordial holes that match this mass and conducted computer simulations to determine the chances of these objects pairing up in binaries that collide. The results were almost a perfect match to LIGO's detection rate so far.
"It's a plausibility argument, which, at the moment, you cannot disprove," said Peter Meszaros, an astronomer at Pennsylvania State University who did not participate in the current study.
Further research will need to investigate the hypothesis to reveal a definitive answer, although Bird entertains the idea that both astrophysical and primordial collisions could be taking place.
"I wouldn't be hugely surprised if it turns out that some of the mergers are astrophysical and some of them are from primordial black holes," he said.
The findings were published March 1 on pre-print server arXiv.
