Black holes in the low-mass gap: Implications for gravitational-wave observations

Anuradha Gupta, Davide Gerosa, K. G. Arun, Emanuele Berti, Will M. Farr, and B. S. Sathyaprakash

Phys. Rev. D 101, 103036 – Published 26 May 2020

Abstract

Binary neutron-star mergers will predominantly produce black-hole remnants of mass $\sim 3 - 4 M_{⊙}$ , thus populating the putative low-mass gap between neutron stars and stellar-mass black holes. If these low-mass black holes are in dense astrophysical environments, mass segregation could lead to “second-generation” compact binaries merging within a Hubble time. In this paper, we investigate possible signatures of such low-mass compact binary mergers in gravitational-wave observations. We show that this unique population of objects, if present, will be uncovered by the third-generation gravitational-wave detectors, such as Cosmic Explorer and Einstein Telescope. Future joint measurements of chirp mass $M$ and effective spin $χ_{eff}$ could clarify the formation scenario of compact objects in the low-mass gap. As a case study, we show that the recent detection of GW190425 (along with GW170817) favors a double Gaussian mass model for neutron stars, under the assumption that the primary in GW190425 is a black hole formed from a previous binary neutron-star merger.

Received 24 January 2020
Accepted 5 May 2020

DOI:https://doi.org/10.1103/PhysRevD.101.103036

Physics Subject Headings (PhySH)

Gravitational waves

Gravitation, Cosmology & Astrophysics

Authors & Affiliations

Anuradha Gupta ^1,2,*, Davide Gerosa ^3,†, K. G. Arun ^4,2,‡, Emanuele Berti ^5,§, Will M. Farr ^6,7,∥, and B. S. Sathyaprakash ^2,8,9,¶

¹Department of Physics and Astronomy, The University of Mississippi, Oxford, Mississippi 38677, USA
²Institute for Gravitation and the Cosmos, Department of Physics, Pennsylvania State University, University Park, Pennsylvania, 16802, USA
³School of Physics and Astronomy & Institute for Gravitational Wave Astronomy, University of Birmingham, Birmingham, B15 2TT, United Kingdom
⁴Chennai Mathematical Institute, Siruseri, India
⁵Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, USA
⁶Center for Computational Astrophysics, Flatiron Institute, 162 Fifth Ave, New York, New York 10010, USA
⁷Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794, USA
⁸Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, Pennsylvania, 16802, USA
⁹School of Physics and Astronomy, Cardiff University, Cardiff, CF24 3AA, United Kingdom

^*agupta1@olemiss.edu
^†d.gerosa@bham.ac.uk
^‡kgarun@cmi.ac.in
^§berti@jhu.edu
^∥will.farr@stonybrook.edu
^¶bss25@psu.edu

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Vol. 101, Iss. 10 — 15 May 2020

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Physical Review D

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