GW190521 produced a black hole remnant estimated at about 142 solar masses.
The LIGO and Virgo collaborations announced GW190521 in 2020. The signal came from the merger of two black holes, estimated at roughly 85 and 66 solar masses before the collision. Their merger produced a remnant near 142 solar masses, with the remainder carried away mainly as gravitational-wave energy.
This event was important because the inferred primary black hole lies in the pair-instability mass gap predicted by some stellar-evolution models. Ordinary massive-star collapse is expected to be difficult in that range, so the event raised the possibility of hierarchical mergers or other formation pathways.
GW190521 was brief and relatively difficult to interpret compared with some earlier signals. Its distance was estimated at billions of light-years. The event did not prove one unique formation scenario, but it provided a striking test of black-hole populations and models of stellar death.