GW190521: A Binary Black Hole Merger with a Total Mass of 150 M_{⊙}. - Abbott R; Abbott TD; Abraham S; Acernese F; Ackley K; Adams C; Adhikari RX; Adya VB; Affeldt C; Agathos M; Agatsuma K; Aggarwal N; et al. (Physical review letters, 2020)