Study shows GW190521 event could be explained by primordial black holes

In September 2020, the LIGO / Virgo collaboration, a large team of scientists working at different universities around the world, announced that they had detected the most massive gravitational wave binary signal observed to date, which they called GW190521. In an article published in Physical examination letters, they explored the hypothesis that this signal was produced by the fusion of two black holes, with at least the mass of the main component in the mass deviation predicted by the supernova theory of pair instability.

Researchers at the University of Geneva, Technion, Sapienza University, and INFN recently examined the LIGO / Virgo data in more detail and explored another explanation for the GW190521 event. In their article, also published in Physical examination letters, they specifically considered the possibility that the GW190521 event could be associated with primordial black holes, those produced in the early universe.

“Our article was born from the observation by the LIGO / Virgo collaboration of the event known as GW190521, the fusion of two black holes,” Antonio Riotto, one of the researchers who conducted the study, told Phys. org. “The most massive black hole happens to be in the so-called mass gap, that is, in a range of masses where astrophysical arguments are insufficient to explain the astrophysical nature of such a black hole. Our main goal was to understand whether the event could have an explanation in the primordial black hole scenario, that is, by those black holes that are generated in the early universe and whose masses can fall into the ‘mass deviation without any problem. “

To examine the possibility that a signal is associated with the so-called primordial black hole scenario, one can calculate the rate at which two black holes of primordial origin merge (i.e. their rate of fusion) to produce a signal. gravitational wave. Next, the researchers must compare this prediction with the rate of fusion that would be necessary to explain the observed signal.

“By matching such a prediction to the observed rate necessary to explain the GW190521 event, we found the parameters of the scenario [that were] necessary and checked whether they escaped the current constraints of other experiments, for example those of microwave cosmic background (CMB) constraints, ”said Riotto.

Riotto and his colleagues demonstrated that the GW190521 event observed by the LIGO / Virgo collaboration could be theoretically explained by the fusion of primordial black holes. In the future, their work could inform other studies aimed at confirming the existence of primordial black holes. Meanwhile, the researchers plan to explore the possibility that other events detected by the LIGO / Virgo collaboration originate from primordial black holes.

“As part of the ongoing effort to establish the existence of primordial black holes using current and future gravitational wave data, we hosted a workshop bringing together scientists studying black holes from the primordial and astrophysical communities, as well as members of LIGO. / Virgo collaboration, with the aim of creating synergies between experts from different fields, ”Gabriele Franciolini, another researcher involved in the study, told Phys.org. “With more than 300 participants, the large participation proves the general interest of the scientific community for this exciting line of research.

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