Study shows that the GW190521 event can be explained by primordial black holes

In September 2020, the LIGO / Virgo collaboration, a large group of scientists working at various universities worldwide, announced that they were observing the most massive gravitational wave binary signal ever observed, which they named GW190521. In an article published in Physical overview letters, they investigated the hypothesis that this signal was produced by the fusion of two black holes, with at least the primary component mass in the mass gap predicted by the pair instability supernova theory.

Researchers at the Université de Genève, Technion, Sapienza University and INFN recently further investigated the LIGO / Virgo data and investigated an alternative explanation for the GW190521 event. In their paper, also published in Physical overview letters, they specifically considered the possibility that the GW190521 event could be linked to original black holes, produced in the early universe.

“Our paper was created by the observation by the LIGO / Virgo collaboration of the so-called GW190521 event, the fusion of two black holes,” Antonio Riotto, one of the researchers who conducted the study, told Phys.org said. “The more massive black hole appears to be in the so-called mass gap, that is, in a series of masses where astrophysical arguments are lacking to explain the astrophysical nature of such a black hole. Our primary goal was to understand whether the ‘event can have a statement within the primordial black-hole scenario, that is, through the black holes generated in the early universe and whose masses can fall into the mass gap without any problem.’

To investigate 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 original origin merge (i.e., their fusion rate) to produce a gravitational wave signal. Next, researchers should compare this prediction with the merger rate needed to explain the observed signal.

“To match such a prediction to the observed rate required to explain the GW190521 event, we found the parameters of the scenario [that were] needed and checked whether they escaped the current limitations of other experiments, for example those of cosmic microwave background (CMB) limitations, “Riotto said. Indeed, it appears that the GW190521 event can be explained by our initial primordial hypothesis of the black hole. “

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

“As part of the ongoing effort to determine the existence of original black holes using current and future gravitational wave data, we have organized a workshop that brings together scientists studying black holes from both the primordial and astrophysical communities, as well as members of the 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 great participation proves the great interest of the scientific community in this exciting line of research.”

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