Illustration of the merger of two boson stars Photograph:( Twitter )
The study shows that the heaviest black hole collision ever observed, produced by the gravitational-wave GW190521, might actually be something even more mysterious: the merger of two boson stars
Astronomers have identified eerie stars of 'dark matter' that were behind the largest gravitational wave, in a recent study.
The study published in Physics Review Letters led by the Galician Institute of High Energy Physics (IGFAE) and the University of Aveiro shows that the heaviest black hole collision ever observed, produced by the gravitational-wave GW190521, might actually be something even more mysterious: the merger of two boson stars.
This would be the first evidence of the existence of these hypothetical objects that constitute one of the main candidates to form dark matter, which makes up 27 per cent of the Universe.
Gravitational waves are ripples in the fabric of spacetime that travel at the speed of light. These originate in the most violent events of our Universe, carrying information about their sources.
Since 2015, mankind can detect and interpret gravitational waves thanks to the two LIGO detectors (Livingston and Hanford, USA) and Virgo (Cascina, Italy) detectors. To date, these detectors have already observed around 50 gravitational-wave signals.
All of these were originated in the collision and merger of two of the most mysterious entities in the Universe, black holes and neutron stars, allowing us to deepen in our knowledge about these objects.
The team compared the GW190521 signal to computer simulations of boson-star mergers and found that these actually explain the data slightly better than the analysis conducted by LIGO and Virgo. The result implies that the source would have different properties than stated earlier.
According to Dr Calderón Bustillo: “First, we would not be talking about colliding black holes anymore, which eliminates the issue of dealing with a forbidden black hole. Second, because boson star mergers are much weaker, we infer a much closer distance than the one estimated by LIGO and Virgo. This leads to a much larger mass for the final black hole, of about 250 solar masses, so the fact that we have witnessed the formation of an intermediate-mass black hole remains true”.
Dr. Nicolás Sanchis-Gual, explains: “Boson stars are objects almost as compact as black holes but, unlike them, do not have a “no-return” surface. When they collide, they form a boson star that can become unstable, eventually collapsing to a black hole, and producing a signal consistent with what LIGO and Virgo observed. Unlike regular stars, which are made of what we commonly know as matter, boson stars are made up of what we know as ultralight bosons. These bosons are one of the most appealing candidates for constituting what we know as dark matter”.
The team found that even though the analysis tends to favour “by design” the merging black-holes hypothesis, a boson star merger is actually preferred by the data, although in a non-conclusive way. Prof. Jose A. Font from the University of Valencia says “Our results show that the two scenarios are almost indistinguishable given the data, although the exotic boson-star one is slightly preferred. This is very exciting since our boson-star model is as of now very limited and subject to major improvements. A more evolved model may lead to even larger evidence for this scenario and would also allow us to study previous gravitational-wave observations under the boson-star merger assumption”.
Professor Carlos Herdeiro, from the University of Aveiro, says that “one of the most fascinating results is that we can actually measure the mass of this putative new dark-matter particle and that a value of zero is discarded with high confidence. If confirmed by subsequent analysis of this and other gravitational-wave observations, our result would provide the first observational evidence for a long-sought dark matter candidate”.