Close Encounters of Tight Binary Stars with Stellar-mass Black Holes

Abstract

Strong dynamical interactions among stars and compact objects are expected in a variety of astrophysical settings, such as star clusters and the disks of active galactic nuclei. Via a suite of 3D hydrodynamics simulations using the moving-mesh code AREPO, we investigate the formation of transient phenomena and their properties in close encounters between an $2M_{\odot }$ or $20M_{\odot }$ equal-mass circular binary star and single $20M_{\odot }$ black hole (BH). Stars can be disrupted by the BH during dynamical interactions, naturally producing electromagnetic transient phenomena. Encounters with impact parameters smaller than the semimajor axis of the initial binary frequently lead to a variety of transients whose electromagnetic signatures are qualitatively different from those of ordinary disruption events involving just two bodies. These include the simultaneous or successive disruptions of both stars and one full disruption of one star accompanied by successive partial disruptions of the other star. On the other hand, when the impact parameter is larger than the semimajor axis of the initial binary, the binary is either simply tidally perturbed or dissociated into bound and unbound single stars ("micro-Hills" mechanism). The dissociation of $20M_{\odot }$ binaries can produce a runaway star and an active BH moving away from one another. Also, the binary dissociation can either produce an interacting binary with the BH, or a non-interacting, hard binary; both could be candidates of BH high- and low-mass X-ray binaries. Hence our simulations especially confirm that strong encounters can lead to the formation of the (generally difficult to form) BH low-mass X-ray binaries.

13 pages, 8 figures, 2 tables. Accepted for publication in MNRAS. Movies: https://www.youtube.com/watch?v=DGz2WokfZLA&list=PLxLK3qI02cQeEc3ktlYAOLY4RHVX1V_nZ

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Cited by in corpus (4)

• Stellar Escape from Globular Clusters. I. Escape Mechanisms and Properties at Ejection
• Simulating the tidal disruption of stars by stellar-mass black holes using moving-mesh hydrodynamics
• Close encounters of black hole - star binaries with stellar-mass black holes
• High mass function ellipsoidal variables in the Gaia Focused Product Release: searching for black hole candidates in the binary zoo