GW190521 (initially S190521g)[5] was a gravitational wave signal resulting from the merger of two black holes.

The remaining 9 solar masses were radiated away as energy in the form of gravitational waves.

[8] According to discovery team member Vassiliki Kalogera of Northwestern University, "this is the first and only firm/secure mass measurement of an intermediate mass black hole at the time of its birth ... Now we know reliably at least one way [such objects can form], through the merger of other black holes.

[15] If this explanation is correct, the flare should repeat after about 1.6 years[3] when the intermediate mass black hole again encounters the accretion disk.

[16] According to Matthew Graham, lead astronomer for the study, "This supermassive black hole was burbling along for years before this more abrupt flare.

In our study, we conclude that the flare is likely the result of a black hole merger, but we cannot completely rule out other possibilities.

"[15] While the original LIGO/Virgo data analysis assumed a quasi-circular inspiral waveform model, subsequent publications claimed that this source could have been significantly eccentric.

[17] Using eccentric waveforms based on numerical relativity, Gayathri et al. 2020 found a best fit with