Compact Object Mergers Driven by Gas Fallback

Abstract

Recently, several gravitational wave detections have shown evidence for compact object mergers. However, the astrophysical origin of merging binaries is not well understood. Stellar binaries are typically at much larger separations than what is needed for the binaries to merge due to gravitational wave emission, which leads to the so-called final AU problem. In this Letter we propose a new channel for mergers of compact object binaries which solves the final AU problem. We examine the binary evolution following gas expansion due to a weak failed supernova explosion, neutrino mass loss, core disturbance, or envelope instability. In such situations the binary is possibly hardened by ambient gas. We investigate the evolution of the binary system after a shock has propagated by performing smoothed particle hydrodynamics simulations. We find that significant binary hardening occurs when the gas mass bound to the binary exceeds that of the compact objects. This mechanism represents a new possibility for the pathway to mergers for gravitational wave events.

Searching for eccentricity: signatures of dynamical formation in the first gravitational-wave transient catalogue of LIGO and Virgo

“…The chemically homogeneous pathway bypasses the expansion problem, with both stars remaining relatively compact throughout their entire evolution (de Mink et al 2010;de Mink & Mandel 2016). Ambient gas-driven fallback has also been suggested to harden initially distant binaries (Tagawa et al 2018).…”

Black Hole Mergers from Hierarchical Triples in Dense Star Clusters

“…There have been many proposed formation channels, both in dense stellar environments and in isolation. These include isolated binary stellar evolution of two massive stars either through common-envelope evolution (Dominik et al 2012(Dominik et al , 2013Belczynski et al 2016aBelczynski et al , 2016bSpera et al 2019), chemically homogeneous evolution of close binaries (de Mink & Mandel 2016; Mandel & de Mink 2016), or catalyzed by flyby perturbations in the field (Michaely & Perets 2019, 2020, or dynamical assembly in dense stellar environments, including young and open star clusters (Banerjee 2017(Banerjee , 2018a(Banerjee , 2018b(Banerjee , 2020Di Carlo et al 2019;Santoliquido et al 2020) Hamers et al 2018;Hoang et al 2018;Fragione et al 2019a;Rasskazov & Kocsis 2019;Stephan et al 2019), and in active galactic nucleus (AGN) (Bartos et al 2017;Stone et al 2017;Tagawa et al 2018Tagawa et al , 2020aTagawa et al , 2020bMcKernan et al 2020). Another proposed scenario involves primordial BHs merging in the halos of galaxies (e.g., Bird et al 2016).…”

Signs of eccentricity in two gravitational-wave signals may indicate a sub-population of dynamically assembled binary black holes

“…Using a stricter threshold Abbott et al (2021) counts 44 confirmed BBH mergers. 1998; Ivanova et al 2013;Kruckow et al 2016), chemically homogeneous evolution (e.g., de Mink et al 2010;de Mink & Mandel 2016), stable mass accretion onto a black hole from its stellar companion (van den Heuvel et al 2017;Neijssel et al 2019;Bavera et al 2021), or ambient gas-driven fallback (e.g., Tagawa et al 2018). In contrast, a dynamically assmebled binary does not become bound until the two components have already evolved into compact objects.…”