A fusion of boson stars – a theoretical object that has not yet been observed – could explain the origin of an enigmatic gravitational wave whose detection was announced in September 2020 and was initially attributed to the merger of two black holes.
When the first detection of gravitational waves that Albert Einstein had predicted a century earlier was announced in 2016, scientists assured that a new window was then opened for astrophysics. They argued that these ripples in the fabric of space-time produced by highly energetic events in the universe would allow them to observe or hear the cosmos in a different way, capture new types of celestial objects, and offer clues about the nature of dark matter. Since then, the Advanced LIGO (in the US) and Virgo (in Italy) detectors have captured fifty gravitational waves generated during black hole or neutron star mergers.
However, it is possible that one of them, GW190521, whose detection was announced in September 2020 and initially attributed to the merger of two black holes, has a different and exciting origin, as an international team argues this week in the journal Physical Review Letters. led by Juan Calderón Bustillo, from the Galician Institute of High Energy Physics (IGFAE).
Because it is possible that through gravitational waves the first proof of the existence of an object that until now remained in the field of theory has been obtained: boson stars. “They are dark, they do not produce electromagnetic radiation, unlike normal stars like our Sun, or neutron stars. They are considered exotic compact objects or black hole imitators, because their gravitational effects are similar to those produced by black holes, only that they do not have an event horizon “, defines José Antonio Font, a researcher at the University of Valencia and co-author of this work.
DOUBTS ABOUT THE ORIGIN OF GW190521
When boson stars merge, they form a hypermassive star that becomes unstable and collapses into a black hole, generating a signal identical to the one LIGO and Virgo observed on May 21, 2019.
Thus, the first analysis of the GW190521 signal, published in September 2020, concluded that it was compatible with the merger of two black holes with a mass of 85 and 66 times the mass of the Sun, which resulted in a black hole. end of 142 solar masses. The latter was the first of a new family of black holes, those of intermediate mass. This was a result with important implications, since this category was now considered a kind of missing link between two already known families: stellar mass black holes (which are formed by the collapse of a star) and supermassive ones (which hide in the centers of galaxies, including our own, the Milky Way).
But it did not all add up. As Font explains, the larger of the two black holes involved in that merger, (the one with 85 solar masses), could not be the result of the collapse of a star, which raised doubts about its nature and prompted them to search for new ones. explanations, such as their origin being boson stars, a proposal that agrees with their models.
If indeed, the boson stars are behind that gravitational wave, it would be the first proof of the existence of these hypothetical objects postulated by theoretical physics in the 60s of the 20th century that constitute one of the main candidates to form dark matter. , which represents 27% of the Universe. “The known physics tells us that they can be formed. That they exist in the universe is another story, it is what we are looking for,” he adds.
“Gravitational waves can allow us to discover these types of dark objects. The problem we find ourselves with is that the gravitational radiation associated with the collision of two boson stars (which is what we have analyzed in the article) is very similar to the which would produce a similar collision of two black holes (of the same mass as the corresponding boson stars, of course). ” That is, after comparing GW190521 with computer simulations of boson star mergers, they found that they explain the data slightly better than the analysis carried out by LIGO and Virgo, which means that there is a greater chance that their origin is boson stars. but they cannot rule out that they have been produced by black holes.