Black holes are one of the most worrisome objects in the universe, with such strong gravity that not even light can escape, making them difficult to study.
Now, a team of researchers has taken that concern to the next level, suggesting that very small black holes from the early universe may be responsible for dark matter, a large percentage of the universe’s contents that scientists can’t see.
Dark matter is a catch-all term for the roughly 27% of the universe’s mass that cannot be detected in any instruments humans have yet designed. Instead, the existence of dark matter is explained by its gravitational effects on other matter—for example, on galaxy clusters. There are many candidates for dark matter, including dark photons, axions, and Weakly Interacting Massive Particles (or WIMPs). But another long-standing candidate is a primordial black hole, or a very small black hole from the early universe, that passes through space and is difficult to see because there is nothing significant orbiting it.
The team’s study, published earlier this month in Physical Review Dstates that the mass of the first black hole “would have been large enough for at least one object to cross the solar system within a decade.” So, the team concluded that, these flyby events will be seen as gravitational waves.
The group’s findings were timely; earlier this month, a separate team announced that signatures of dark matter may be lurking in gravitational wave data collected by the Laser Interferometer Gravitational-Wave Observatory, or LIGO.
The idea of some “primitive” black holes refers to the idea that they were born in the early times of the universe, as random fluctuations caused globs of matter to fall in on themselves, creating small and lightless entities. The black holes we can see range from stellar-mass (about the size of the Sun and similar stars) to billions of times that. So a black hole the size of an asteroid is very small in relative terms, yet it can be tiny—even the size of an atom.
where primitive black holes may have formed, and instruments that can detect black holes. Photo: ESA
Sarah Geller, a physicist at the University of California at Santa Cruz and an author of the paper, told LiveScience that “we are not making any of the following claims – that black holes really exist, that they make up most or all of dark matter; or that they really exist in our solar system.” Instead, say the group if all of the above being true, it would mean that one such object would travel through the inner solar system every 10 years.
With new gravitational wave discoveries being made all the time—and LISA, the next-generation gravitational wave observatory currently being assembled—we’re in for an exciting time for classical black holes.
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