TIDAL DISRUPTION RATES IN NON-SPHERICAL GALACTIC NUCLEI FORMED BY GALAXY MERGERS

Abstract

ABSTRACT We explore the rates of tidal disruption events (TDEs) of stars by supermassive black holes (SBHs) in galactic nuclei formed in mergers followed by a formation and coalescence of a binary SBH. Such systems initially have a deficit of stars on low-angular-momentum orbits caused by the slingshot process during the binary SBH stage, which tends to reduce the flux of stars into the SBH compared to the steady-state value. On the other hand, a newly formed galactic nucleus has a non-spherical shape, which enhances the mixing of stars in angular momentum and, thus, the TDE rate. In galaxies with relatively low SBH masses ( ), relaxation times are short enough to wash out the anisotropy in initial conditions, and for more massive SBHs the enhancement of flux due to non-sphericity turns out to be more important than its suppression due to initial anisotropy. Therefore, the present-day TDE rates generally exceed conventional steady-state estimates based on a spherical isotropic approximation. We thus conjecture that the lower observationally inferred TDE rates compared to theoretical predictions cannot be attributed to the depletion of low-angular-momentum stars by SBH binaries.