Physics: discoveries of gravitational waves multiply
In Italy: in the guts of Virgo, the laboratory capable of 'hunting' a gravitational wave a week
Interview with Barry Barish "It wasn't a eureka moment, I panicked"
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 opening 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 the mergers of black holes or neutron stars.
However, it is possible that one of them, GW190521, detected in September 2020 and initially attributed to the merger of two black holes, has a different and exciting origin, as
an international team led by Juan
argues this week in the journal
Physical Review Letters.
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. Boson stars are considered exotic compact objects or
black hole
mimics
, because their gravitational effects are similar to those they produce. black holes, they just don't have an event horizon ", defines José Antonio Font, a researcher at the University of Valencia and co-author of this work, via email.
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 in September 2020.
Thus, the first analysis of the GW190521 signal 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 final black hole of 142 solar masses.
The latter was the first of a new family of black holes, those of intermediate mass.
It 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).
Not everything fitted.
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.
A new particle, the ultralight boson
If indeed, boson stars were the origin of 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 matter. dark, 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 are more possibilities that their origin is the boson stars. but they cannot rule out that they have been produced by black holes.
Likewise, this team has calculated the mass of the fundamental component of these stars, a new particle known as an ultralight boson that is billions of times lighter than an electron.
"
We know, again theoretically, that the type of bosonic particle that could constitute these stars must be similar to the Higgs boson
, although in the case of boson stars it should weigh much less, be ultralight," he details.
For Font, this work must be considered as a proof of concept that shows that using observations of gravitational waves, specifically GW190521, it is possible to provide arguments in favor of other explanations to the origin of the signal, which could have very profound implications and lead to other discoveries, in this case the possible existence of dark stars composed of ultralight bosonic particles, which have also been postulated to explain the mysterious dark matter.
I think that's where the interest of our work lies, which can potentially have profound and quite interesting implications.
Regarding the implications of this proposal for the knowledge of dark matter, Font considers that "we must be prudent. We will see what the future holds and if the model passes new detections. What is certain is that This analysis is proving very fun and exciting and that if at some point it could be seen that the model continues to fit new observations well, there would be stronger arguments to start thinking that perhaps dark matter could be made up of fundamental boson fields. There are several proposals on the table trying to explain what dark matter is: WIMPs, primordial black holes and the ultralight bosons that make up boson stars. "
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