In September 2020, the LIGO/Virgo collaboration, a large team of scientists working at different universities worldwide, announced that they had detected most massive gravitational wave binary signal observed to date, which they called GW190521. In a paper published in Physical Review Letters, they explored the hypothesis that this signal was produced by the merger of two black holes, with at least the primary component mass in the mass gap predicted by the pair-instability supernova theory.