Tidal disruption rate suppression by the event horizon of spinning black holes

TL;DR

This paper investigates how the event horizon of spinning black holes suppresses observable tidal disruption events, and introduces a relativistic criterion to better understand the impact of black hole spin and stellar population age on TDE rates.

Contribution

It extends the frozen-in approximation to a relativistic context and introduces the spin-age degeneracy, enhancing understanding of TDE rate suppression by black hole properties.

Findings

High black hole spin (>0.5) increases TDE observability for massive BHs.

Young stellar populations (<1 Gyr) also increase TDE rates.

The spin-age degeneracy complicates constraining black hole spins from TDE rates.

Abstract

The rate of observable tidal disruption events (TDEs) by the most massive black holes (BHs) is suppressed due to direct capture of stars by the event horizon. This suppression effect depends on the shape of the horizon and holds the promise of probing the spin distribution of dormant BHs at the centers of galaxies. By extending the frozen-in approximation commonly used in the Newtonian limit, we propose a general relativistic criterion for the tidal disruption of a star of given interior structure. The rate suppression factor is then calculated for different BH masses, spins, and realistic stellar populations. We find that either a high BH spin (> 0.5) or a young stellar population (< 1 Gyr) allows TDEs to be observed from BHs significantly more massive than 10^8 solar masses. We call this spin-age degeneracy (SAD). This limits our utility of the TDE rate to constrain the BH spin distribution, unless additional constraints on the age of the stellar population or the mass of the disrupted star can be obtained by modeling the TDE radiation or the stellar spectral energy distribution near the galactic nuclei.