GW190521: Orbital Eccentricity and Signatures of Dynamical Formation in a Binary Black Hole Merger Signal
Abstract
Pairinstability supernovae are thought to restrict the formation of black holes in the mass range $\sim 50\mbox{}135\,{M}_{\odot }$ . However, black holes with masses within this "high mass gap" are expected to form as the remnants of binary black hole mergers. These remnants can merge again dynamically in densely populated environments such as globular clusters. The hypothesis that the binary black hole merger GW190521 formed dynamically is supported by its high mass. Orbital eccentricity can also be a signature of dynamical formation, since a binary that merges quickly after becoming bound may not circularize before merger. In this work, we measure the orbital eccentricity of GW190521. We find that the data prefer a signal with eccentricity $e\geqslant 0.1$ at 10 Hz to a nonprecessing, quasicircular signal, with a log Bayes factor $\mathrm{ln}{ \mathcal B }=5.0$ . When compared to precessing, quasicircular analyses, the data prefer a nonprecessing, $e\geqslant 0.1$ signal, with log Bayes factors $\mathrm{ln}{ \mathcal B }\approx 2$ . Using injection studies, we find that a nonspinning, moderately eccentric (e = 0.13) GW190521like binary can be mistaken for a quasicircular, precessing binary. Conversely, a quasicircular binary with spininduced precession may be mistaken for an eccentric binary. We therefore cannot confidently determine whether GW190521 was precessing or eccentric. Nevertheless, since both of these properties support the dynamical formation hypothesis, our findings support the hypothesis that GW190521 formed dynamically.
 Publication:

The Astrophysical Journal
 Pub Date:
 November 2020
 DOI:
 10.3847/20418213/abbe26
 arXiv:
 arXiv:2009.04771
 Bibcode:
 2020ApJ...903L...5R
 Keywords:

 Black holes;
 Compact objects;
 High energy astrophysics;
 Dynamical evolution;
 Eccentricity;
 Gravitational wave astronomy;
 Gravitational waves;
 Gravitational wave sources;
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 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 7 pages, 2 figures. Accepted for publication in ApJL