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The gravitational-wave signal GW190521 is consistent with a binary black hole (BBH) merger source at redshift 0.8 with unusually high component masses, 85⁺²¹_-14M⊙ and 66⁺¹⁷_-18M⊙, compared to previously reported events, and shows mild evidence for spin-induced orbital precession. The primary falls in the mass gap predicted by (pulsational) pair-instability supernova theory, in the approximate range 65–120 M⊙. The probability that at least one of the black holes in GW190521 is in that range is 99.0%. The final mass of the merger (142⁺²⁸_-16M⊙) classifies it as an intermediate-mass black hole. Under the assumption of a quasi-circular BBH coalescence, we detail the physical properties of GW190521's source binary and its post-merger remnant, including component masses and spin vectors. Three different waveform models, as well as direct comparison to numerical solutions of general relativity, yield consistent estimates of these properties. Tests of strong-field general relativity targeting the merger-ringdown stages of the coalescence indicate consistency of the observed signal with theoretical predictions. We estimate the merger rate of similar systems to be 0.13^+0.30_-0.11Gpc^-3yr^-1. We discuss the astrophysical implications of GW190521 for stellar collapse and for the possible formation of black holes in the pair-instability mass gap through various channels: via (multiple) stellar coalescences, or via hierarchical mergers of lower-mass black holes in star clusters or in active galactic nuclei. We find it to be unlikely that GW190521 is a strongly lensed signal of a lower-mass black hole binary merger. We also discuss more exotic possible sources for GW190521, including a highly eccentric black hole binary, or a primordial black hole binary.

Item Type:	Refereed Article
Keywords:	astrophysical black holes, high energy astrophysics, gravitational collapse, gravitation, gravitational wave astronomy, gravitational wave sources, LIGO, stellar mass black holes, stellar populations, intermediate-mass black holes
Research Division:	Physical Sciences
Research Group:	Astronomical sciences
Research Field:	General relativity and gravitational waves
Objective Division:	Expanding Knowledge
Objective Group:	Expanding knowledge
Objective Field:	Expanding knowledge in the physical sciences
UTAS Author:	Siellez, K (Dr Karelle Siellez)
ID Code:	150362
Year Published:	2020
Web of Science® Times Cited:	214
Deposited By:	Physics
Deposited On:	2022-06-09
Last Modified:	2022-06-09
Downloads:	0