# Stellar binaries in galactic nuclei: tidally stimulated mergers followed by tidal disruptions

## TL;DR

This study explores how stellar binaries near massive black holes in galactic nuclei tend to merge due to tidal interactions, often leading to tidal disruptions, with implications for understanding certain energetic astrophysical phenomena.

## Contribution

It reveals that tidal excitation causes most binaries to merge before tidal separation, highlighting a new pathway for stellar mergers and disruptions in galactic centers.

## Key findings

- Over 75% of binaries merge due to eccentricity excitation.
- Stellar tides circularize binaries, resulting in low-eccentricity mergers.
- Merged stars may be tidally disrupted, explaining some tidal disruption events.

## Abstract

We investigate interactions of stellar binaries in galactic nuclear clusters with a massive black hole (MBH). We consider binaries on highly eccentric orbits around the MBH that change due to random gravitational interactions with other stars in the nuclear stellar cluster. The pericenters of the orbits perform a random walk, and we consider cases where this random walk slowly brings the binary to the Hills tidal separation radius (the so-called empty loss-cone regime). However, we find that in a majority of cases the expected separation does not occur and instead the members of the binary merge together. This happens because the binary's eccentricity is excited by tidal interactions with the MBH, and the relative excursions of the internal eccentricity of the binary far exceed those in its internal semimajor axis. This frequently reduces the pericenter separation to values below typical stellar diameters, which induces a significant fraction of such binaries to merge ($\gtrsim 75\%$ in our set of numerical experiments). Stellar tides do not appreciably change the total rate of mergers but circularise binaries, leading to a significant fraction of low-eccentricity, low-impact-velocity mergers. Some of the stellar merger products will then be tidally disrupted by the MBH within $\sim 10^6$ years. If the merger strongly enhances the magnetic field of the merger product, this process could explain observations of prompt relativistic jet formation in some tidal disruption events.