At least one of the gravitational waves detected by the LIGO and Virgo detectors might not be from black holes or neutron stars, but something even more exotic, physicists have claimed. Known as boson stars or dark matter stars, we have no other evidence these objects even exist. However, they would be useful in explaining some aspects of the universe that don’t currently make sense, as well as the exceptional features of this wave.
However, an additional hope for the detectors was that they would find new objects, whose existence was uncertain or barely guessed at. An international team thinks one detected gravitational wave, GW190521, might have done just that. Their bet is on a merger between two stars made from particles different from those that make up most of the familiar universe.
Bosons are a class of subatomic particles with integer spins. Besides photons, which we know well, and the
“Boson stars behave very much like black holes but they are fundamentally different, as they lack the two most distinctive (and somewhat problematic) aspects of black holes: their no-return surface known as event horizon, and the singularity in the interior, where laws of physics break down,” said study author Dr Sanchis-Gual of the University of Valencia in a
If so, we might not be able to see such stars – but their mass could contribute to the explanation for the
The challenge would be distinguishing such a wave from one produced by two black holes. But one wave is thought to show the signs.
When GW190521 was first detected it was announced as the product of the two heaviest (and most distant) black holes we had yet seen merging, with a combined mass of 142 times that of the Sun.
However, details of the event puzzled astronomers. For one thing, the location appeared to be
In two papers, Sanchis-Gaul and co-authors propose GW190521’s components are more likely to have been boson stars than black holes. They argue that the methods currently used to process gravitational waves are designed on the assumption that anything contributing to a wave, and larger than a certain mass, is a black hole. By scrapping these assumptions and simulating what would happen if boson stars merged, the team produced an outcome similar to GW190521. They also provide evidence another gravitational wave, GW190426, was not produced by boson stars, while GW200220 probably wasn’t either.
The fact a simulation matches the observation doesn’t prove GW190521 was a boson star merger, or even that boson stars exist. Alternative explanations for GW190521
A paper on how the authors searched for signs of boson stars in specific gravitational waves is published in the journal
A more general discussion on how to process gravitational wave data to allow for more possibilities is published open access in the journal