The Laser Interferometer Gravitational-wave Observatory (LIGO) has been one nifty new astronomical tool. In its brief existence, it has been able to detect several of the elusive gravitational waves. Previously, these had just been the stuff of speculations.
Now, these new discoveries could be key to identifying another astronomical speculation: dark matter. Two papers published in Physical Review Letters posit that the black holes that produced the first LIGO-detected gravitational waves could explain the nature of dark matter in the universe.
Dark matter is the speculative substance that astronomers say makes up most of the mass of the universe and is what holds galaxies and clusters together. Conventional theories say that this matter is made up of unidentified particles. But the data from LIGO may prove that it actually originated in primordial black holes.
A Few Theories
Primordial black holes are those that are not formed by collapsing stars, but dense regions of the early universe that collapsed in on themselves.
Earlier this month, a Japanese team reported that the black holes LIGO detected may be primordial, and that they may make up some portion of the universe’s dark matter-- although this would make up but a small fraction of dark matter. Back in May, a team from John Hopkins discovered that the rate of black hole mergers LIGO estimated was the same as that of the primordial black hole dark matter.
Previous research has shown that the primordial black hole dark matter could only be possible for a very specific set of masses. But that range of masses corresponds neatly with the masses of the black holes LIGO found. The John Hopkins team saw that if primordial black holes were the source of dark matter, the estimated rate of LIGO seeing merging primordial black holes was the same as LIGO’s estimated detection rate. Although both estimates have large errors, their agreement indicates that dark matter may be composed of primordial black holes.
Ultimately, more LIGO detections would have to be made in order to confirm these theories.