Fallback rates in partial tidal disruptions of white dwarfs by intermediate mass black holes

TL;DR

This study uses numerical simulations to analyze the fallback rates of debris after partial tidal disruptions of white dwarfs by intermediate mass black holes, revealing that the fallback rate depends on core mass and differs from supermassive black hole cases.

Contribution

It provides the first detailed numerical analysis of partial tidal disruptions of white dwarfs by IMBHs, showing the fallback rate's dependence on core mass and challenging previous conjectures.

Findings

Fallback rate does not follow the $t^{-9/4}$ power law for IMBHs.

Fallback rate is strongly dependent on the core mass fraction.

Derived a formula for late-time fallback rate based on core mass.

Abstract

Fallback rate of debris after a partial tidal disruption event of a star with an intermediate mass black hole (IMBH) might provide important signatures of such black holes, compared to supermassive ones. Here using smoothed particle hydrodynamics methods, we provide a comprehensive numerical analysis of this phenomenon. We perform numerical simulations of single partial tidal disruptions of solar mass white dwarfs in parabolic orbits, with a non-spinning $10^3M_{\odot}$ IMBH for various values of the impact parameter, and determine the core mass fractions and fallback rates of debris into the IMBH. For supermassive black holes, in a full disruption processes, it is known that the late time fallback rate follows a power law $t^{-5/3}$, whereas for partial disruptions, such a rate has been recently conjectured to saturate to a steeper power law $t^{-9/4}$, independent of the mass of the remnant core. We show here that for IMBHs, partial disruptions significantly alter this conclusion. That is, the fallback rate at late times do not asymptote to a $t^{-9/4}$ power law, and this rate is also a strong function of the core mass. We derive a robust formula for the late time fallback rate as a function of the core mass fraction, that is independent of the white dwarf mass, as we verify numerically by varying the mass of the white dwarf.