Letter to the Editor

Explodability fluctuations of massive stellar cores enable asymmetric compact object mergers such as GW190814

¹ Institute of Astrophysics, Foundation for Research and Technology–Hellas, N. Plastira 100, Voutes 71003, Greece
e-mail: john@ia.forth.gr
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁴ DARK, Niels Bohr Institute, University of Copenhagen, Jagtvej 128, 2200 Copenhagen, Denmark
⁵ Niels Bohr International Academy, The Niels Bohr Institute, Blegdamsvej 17, 2100 Copenhagen, Denmark
⁶ Jodrell Bank Centre for Astrophysics, University of Manchester, Manchester M13 9PL, UK
⁷ School of Physics and Astronomy, Monash University, Clayton, VIC 3800, Australia
⁸ Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus, Denmark

Received: 28 September 2021
Accepted: 1 December 2021

Abstract

The first three observing runs with Advanced LIGO and Virgo have resulted in the detection of binary black hole (BBH) mergers with highly unequal mass components, which are difficult to reconcile with standard formation paradigms. The most representative of these is GW190814, a highly asymmetric merger between a 23 M_⊙ black hole (BH) and a 2.6 M_⊙ compact object. Here, we explore recent results, suggesting that a sizable fraction of stars with pre-collapse carbon-oxygen core masses above 10 M_⊙, and extending up to at least 30 M_⊙, may produce objects inside the so-called lower mass gap that bridges the division between massive pulsars and BHs in Galactic X-ray binaries. We demonstrate that such an explosion landscape would naturally cause a fraction of massive binaries to produce GW190814-like systems instead of symmetric-mass BBHs. We present examples of specific evolutionary channels leading to the formation of GW190814 and GW200210, a 24 + 2.8 M_⊙ merger discovered during the O3b observing run. We estimate the merger-rate density of these events in our scenario to be 𝒪(5%) of the total BBH merger rate. Finally, we discuss the broader implications of this formation channel for compact object populations, and its possible relevance to less asymmetric merger events such as GW200105 and GW200115.