Rates of Stellar Tidal Disruption Events around Intermediate-mass Black Holes

Abstract

Rates of stellar tidal disruption events (TDEs) around supermassive black holes (SMBHs) have been extensively calculated using the loss cone theory, while theoretical work on TDE rates around intermediate-mass black holes (IMBHs) has been lacking. In this work, we aim to accurately calculate the IMBH TDE rates based on their black hole (BH) masses and the stellar profiles of their host galaxies obtained from the latest observations. We find that the TDE rate per galaxy for IMBHs in the center of small galaxies is similar to that of SMBH TDEs, while the TDE rate per cluster from IMBHs in globular clusters is much lower. Very interestingly, we show that the rate of IMBH TDEs generally increases with the BH mass, which is opposite to the trend seen in SMBH TDEs. As a result, the volumetric TDE rate peaks around a BH mass of 106 M⊙. The IMBH TDEs from galactic nuclei have an overall volumetric rate comparable to SMBH TDEs at ∼10−7 Mpc−3 yr−1, and off-center IMBH TDEs from globular clusters have a volumetric rate that is one or two orders of magnitude lower, assuming that their occupation fraction varies within 10%–100%. Furthermore, we report that IMBH TDEs typically occur in the pinhole regime, which means that deeply plunging events are more likely for IMBH TDEs compared to SMBH TDEs.