Ionization and dissociation induced fragmentation of a tidally disrupted star into planets around a supermassive black hole

TL;DR

This study uses radiation hydrodynamics simulations to show that stars tidally disrupted by supermassive black holes can fragment into planet-like clumps due to ionization and dissociation processes, potentially forming planets around black holes.

Contribution

It introduces a novel mechanism of fragmentation caused by ionization and dissociation during tidal disruption, leading to planet formation near supermassive black holes.

Findings

Disrupted stars form approximately 20 clumps of 0.1 to 12 Jupiter masses.

Mass fallback rate exhibits spikes indicating clump formation.

Unbound debris clumps could become free-floating planets or brown dwarfs.

Abstract

We show results from the radiation hydrodynamics (RHD) simulations of tidal disruption of a star on a parabolic orbit by a supermassive black hole (SMBH) based on a three-dimensional smoothed particle hydrodynamics code with radiative transfer. We find that such a tidally disrupted star fragment and form clumps soon after its tidal disruption. The fragmentation results from the endothermic processes of ionization and dissociation that reduce the gas pressure, leading to local gravitational collapse. Radiative cooling is less effective because the stellar debris is still highly optically thick in such an early time. Our simulations reveal that a solar-type star with a stellar density profile of n=3 disrupted by a 10^6 solar mass black hole produces $\sim20$ clumps of masses in the range of 0.1 to 12 Jupiter masses. The mass fallback rate decays with time, with pronounced spikes from early to late time. The spikes provide evidence for the clumps of the returning debris, while the clumps on the unbound debris can be potentially freely-floating planets and brown dwarfs. This ionization and dissociation induced fragmentation on a tidally disrupted star are a promising candidate mechanism to form low-mass stars to planets around an SMBH.