Tidal Disruption of Inclined or Eccentric Binaries by Massive Black Holes

TL;DR

This paper investigates how inclined and eccentric binary stars are tidally disrupted by massive black holes, revealing angular dependencies and providing models for disruption probabilities and ejection velocities.

Contribution

It offers new insights into the disruption probabilities of inclined and eccentric binaries near black holes, including numerical fits and angular dependence analysis.

Findings

Deep penetrators disrupt all binaries with specific orientations.

Perpendicular binary axes have higher survival chances (~20%).

Retrograde eccentric binaries have increased disruption and ejection velocities.

Abstract

Binary stars that are on close orbits around massive black holes (MBH) such as Sgr A* in the center of the Milky Way are liable to undergo tidal disruption and eject a hypervelocity star. We study the interaction between such a MBH and circular binaries for general binary orientations and penetration depths (i.e. binaries penetrate into the tidal radius around the BH). We show that for very deep penetrators, all binaries are disrupted when the binary rotation axis is roughly oriented toward the BH or it is in the opposite direction. The surviving chance becomes significant when the angle between the binary rotation axis and the BH direction is between \pi /4 and 3 \pi /4. The surviving chance is as high as $\sim$ 20$\%$ when the binary rotation axis is perpendicular to the BH direction. The angular dependence is opposite for very shallow penetrators where coplanar prograde orbits have the lowest surviving chance (or equivalently most vulnerable). We provide numerical fits to the disruption probability and energy gain at the the BH encounter as a function of the penetration depth. The latter can be simply rescaled in terms of binary masses, their initial separation and the binary-to-BH mass ratio to evaluate the ejection velocity of a binary members in various systems. We also investigate the disruption of coplanar, eccentric binaries by a MBH. It is shown that for highly eccentric binaries retrograde orbits have a significantly increased disruption probability and ejection velocities compared to the circular binaries.