Relativistic tidal compressions of a star by a massive black hole

TL;DR

This paper models the relativistic tidal compression of a star by a supermassive black hole, revealing shock wave formation and potential observable high-energy emissions during close encounters.

Contribution

It introduces a relativistic hydrodynamical simulation of stellar compression near a black hole, highlighting multiple shock waves and their observational signatures.

Findings

Multiple shock waves form during stellar compression.

Shock waves heat the star's surface to high energies.

Results are consistent with observed gamma-ray bursts.

Abstract

Aims: We investigate the stellar pancake mechanism during which a solar-type star is tidally flattened within its orbital plane passing close to a 10^6 solar masses black hole. We simulate the relativistic orthogonal compression process and follow the associated shock waves formation. Methods: We consider a one-dimensional hydrodynamical stellar model moving in the relativistic gravitational field of a non-rotating black hole. The model is numerically solved using a Godunov-type shock-capturing source-splitting method in order to correctly reproduce the shock waves profiles. Results: Simulations confirm that the space-time curvature can induce several successive orthogonal compressions of the star which give rise to several strong shock waves. The shock waves finally escape from the star and repeatedly heat up the stellar surface to high energy values. Such a shock-heating could interestingly provide a direct observational signature of strongly disruptive star - black hole encounters through the emission of hard X or soft gamma-ray bursts. Timescales and energies of such a process are consistent with some observed events such as GRB 970815.