Tidal Disruptions of White Dwarfs from Ultra-Close Encounters with Intermediate Mass Spinning Black Holes

TL;DR

This study uses numerical relativity to analyze tidal disruptions of white dwarfs by spinning intermediate mass black holes, revealing how black hole spin affects debris dynamics, accretion, and observable signals.

Contribution

It provides the first full general relativistic simulations of white dwarf tidal disruptions by spinning black holes, detailing the impact of spin orientation on debris and accretion.

Findings

Disruption process depends on black hole spin magnitude and orientation.

Late-time accretion follows a t^{-5/3} decay similar to Newtonian predictions.

Disrupted material is scattered by frame dragging, affecting observability.

Abstract

We present numerical relativity results of tidal disruptions of white dwarfs from ultra-close encounters with a spinning, intermediate mass black hole. These encounters require a full general relativistic treatment of gravity. We show that the disruption process and prompt accretion of the debris strongly depend on the magnitude and orientation of the black hole spin. However, the late-time accretion onto the black hole follows the same decay, $\dot{M}$ ~ t^{-5/3}, estimated from Newtonian gravity disruption studies. We compute the spectrum of the disk formed from the fallback material using a slim disk model. The disk spectrum peaks in the soft X-rays and sustains Eddington luminosity for 1-3 yrs after the disruption. For arbitrary black hole spin orientations, the disrupted material is scattered away from the orbital plane by relativistic frame dragging, which often leads to obscuration of the inner fallback disk by the outflowing debris. The disruption events also yield bursts of gravitational radiation with characteristic frequencies of ~3.2 Hz and strain amplitudes of ~10^{-18} for galactic intermediate mass black holes. The optimistic rate of considered ultra-close disruptions is consistent with no sources found in ROSAT all-sky survey. The future missions like Wide-Field X-ray Telescope (WFXT) could observe dozens of events.