Dynamical Formation Scenarios for GW190521 and Prospects for Decihertz Gravitational-Wave Astronomy with GW190521-Like Binaries

TL;DR

This paper explores the formation and detectability of GW190521-like black hole binaries, highlighting how their eccentricity impacts observations across different gravitational-wave detectors and emphasizing the potential of decihertz observatories for detailed characterization.

Contribution

It demonstrates that dynamically formed GW190521-like binaries can have significant eccentricity and may bypass the LISA band, advocating for decihertz detectors to better constrain their properties.

Findings

GW190521-like binaries may have eccentricities up to 0.7 at 10Hz.

Dynamically formed binaries can skip the LISA band entirely.

Decihertz observatories can improve eccentricity measurements significantly.

Abstract

The gravitational-wave (GW) detection of GW190521 has provided new insights on the mass distribution of black holes and new constraints for astrophysical formation channels. With independent claims of GW190521 having significant pre-merger eccentricity, we investigate what this implies for GW190521-like binaries that form dynamically. The Laser Interferometer Space Antenna (LISA) will also be sensitive to GW190521-like binaries if they are circular from an isolated formation channel. We show, however, that GW190521-like binaries that form dynamically may skip the LISA band entirely. To this end, we simulate GW190521 analogues that dynamically form via post-Newtonian binary-single scattering. From these scattering experiments, we find that GW190521-like binaries may enter the LIGO-Virgo band with significant eccentricity as suggested by recent studies, though well below an eccentricity of $e_{\rm 10Hz} \lesssim 0.7$. Eccentric GW190521-like binaries further motivate the astrophysical science case for a decihertz GW observatory, such as the kilometer-scale version of the Midband Atomic Gravitational-wave Interferometric Sensor (MAGIS). Pre-merger observations of GW190521-like binaries with such a decihertz GW detector would be able to constrain the eccentricity of GW190521-like binaries to greater precision than with just LIGO-Virgo alone. These eccentricity constraints would also provide additional insights into the possible environments that GW190521-like binaries form in.