Tidal breakup of quadruple stars in the Galactic Centre

Abstract

The most likely origin of hypervelocity stars (HVSs) is the tidal disruption of a binary star by the supermassive black hole (MBH) in the Galactic Centre (GC). However, HE0437-5439, a $9$ M${}_{\odot }$ B-type main-sequence star moving with a heliocentric radial velocity of about $720$ km s${}^{-1}$ at a distance of $\sim 60$ kpc, and the recent discovered hypervelocity binary candidate (HVB), traveling at $\sim 570$ km s${}^{-1}$, challenge this standard scenario. Recently, Fragione & Gualandris (2018) have demonstrated that the tidal breakup of a triple star leads to an insufficient rate. Observations show that quadruple stars made up of two binaries orbiting their common center of mass (the so-called 2+2 quadruples) are $\approx 4\%$ of the stars in the solar neighborhood. Although rarer than triples, 2+2 quadruple stars may have a role in ejecting HVBs as due to their larger energy reservoir. We present a numerical study of 2+2 quadruple disruptions by the MBH in the GC and find that the production of HVBs has a probability $\lesssim 2-4\%$, which translates into an ejection rate of $\lesssim 1$ Gyr${}^{-1}$, comparable to the triple disruption scenario. Given the low ejection rate, we suggest that alternative mechanisms are responsible for the origin of HVBs, as the ejection from the interaction of a young star cluster with the MBH in the GC and the origin in the Large Magellanic Cloud.

9 pages, 6 Figures, 2 Tables, post-referee version

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Cited by in corpus (8)

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• Hypervelocity Stars from a Supermassive Black Hole-Intermediate-mass Black Hole binary
• Massive binary star mergers in galactic nuclei: implications for blue stragglers, binary S-stars and gravitational waves
• Hypervelocity stars from star clusters hosting Intermediate-Mass Black Holes
• Hypervelocity binaries from close encounters with a SMBH-IMBH binary: orbital properties and diagnostics
• Supernovae in massive binaries and compact object mergers near supermassive black holes