Relativistic Tidal Disruption and Nuclear Ignition of White Dwarf Stars by Intermediate Mass Black Holes

TL;DR

This study uses general relativistic simulations to explore how white dwarf stars are tidally disrupted by intermediate mass black holes, triggering nuclear reactions that produce diverse elements and generate detectable gravitational waves.

Contribution

It provides the first detailed relativistic modeling of white dwarf tidal disruptions by intermediate mass black holes, highlighting nuclear ignition and element synthesis outcomes.

Findings

Nuclear ignition occurs even at weak tidal interactions.

Calcium to iron ratio inversely correlates with tidal strength.

Gravitational waves from these events are detectable at 10 Mpc.

Abstract

We present results from general relativistic calculations of the tidal disruption of white dwarf stars from near encounters with intermediate mass black holes. We follow the evolution of 0.2 and $0.6 M_\odot$ stars on parabolic trajectories that approach $10^3$ - $10^4 M_\odot$ black holes as close as a few Schwarzschild radii at periapsis, paying particular attention to the effect tidal disruption has on thermonuclear reactions and the synthesis of intermediate to heavy ion elements. These encounters create diverse thermonuclear environments characteristic of Type I supernovae and capable of producing both intermediate and heavy mass elements in arbitrary ratios, depending on the strength (or proximity) of the interaction. Nuclear ignition is triggered in all of our calculations, even at weak tidal strengths $\beta \sim 2.6$ and large periapsis radius $R_P \sim 28$ Schwarzschild radii. A strong inverse correlation exists between the mass ratio of calcium to iron group elements and tidal strength, with $\beta \lesssim 5$ producing predominately calcium-rich debris. At these moderate to weak interactions, nucleosynthesis is not especially efficient, limiting the total mass and outflows of calcium group elements to $< 15$\% of available nuclear fuel. Iron group elements however continue to be produced in greater quantity and ratio with increasing tidal strength, peaking at $\sim 60$\% mass conversion efficiency in our closest encounter cases. These events generate short bursts of gravitational waves with characteristic frequencies 0.1-0.7 Hz and strain amplitudes $0.5\times10^{-22}$ - $3.5\times10^{-22}$ at 10 Mpc source distance.