GW190521 and the Primordial Black Hole Scenario
In an article recently published in Physical Review Letters, an international collaboration between the University of Geneve (CH), Technion (IL), and Sapienza University of Rome discusses the possibility that GW190521, one of the gravitational-wave signals detected by the LIGO/Virgo Collaboration during the latest observational run, is of primordial origin.
GW190521 is the first binary black hole merger with at least the primary component mass in the mass gap predicted in the standard astrophysical scenario in which black holes are formed as the final state of stellar evolution, thus motivating alternative hypotheses. In this recent letter, the authors show that GW190521 cannot be explained within the primordial black hole scenario (in which black holes would be formed during inflation in th early universe) if these black holes do not accrete during their cosmological evolution, since this would require an abundance which is already in tension with current constraints on primordial black holes. On the other hand, GW190521 may have a primordial origin if primordial black holes accrete efficiently before the reionization epoch.
The possibility that some of the LIGO/Virgo events are actually primordial black holes is an active field of research and it's the main topic of the workshop "Primordial Black Holes Confront Gravitational-Wave Data" originally organized at Sapienza and now remotely on Zoom (Feb 8-12, 2021). The workshop will bring together around 300 experts on gravitational-wave sources and modelling, primordial black hole formation and evolution, and cosmology, to discuss how the primordial scenario confronts current and future GW data.