Star Formation Around Super-Massive Black Holes

TL;DR

This paper presents numerical simulations showing how giant molecular clouds can infall and form eccentric, star-forming discs around supermassive black holes, explaining observed young stellar rings.

Contribution

It introduces a new model of star formation via cloud infall and fragmentation near black holes, accounting for eccentric stellar orbits and top-heavy mass distributions.

Findings

Simulations produce eccentric stellar discs around black holes.

Star formation occurs at high temperatures, favoring massive stars.

Multiple stellar rings can form repeatedly through this process.

Abstract

The presence of young massive stars orbiting on eccentric rings within a few tenths of a parsec of the supermassive black hole in the Galactic centre is challenging for theories of star formation. The high tidal shear from the black hole should tear apart the molecular clouds that form stars elsewhere in the Galaxy, while transporting the stars to the Galactic centre also appears unlikely during their stellar lifetimes. We present numerical simulations of the infall of a giant molecular cloud that interacts with the black hole. The transfer of energy during closest approach allows part of the cloud to become bound to the black hole, forming an eccentric disc that quickly fragments to form stars. Compressional heating due to the black hole raises the temperature of the gas to 100-1000K, ensuring that the fragmentation produces relatively high stellar masses. These stars retain the eccentricity of the disc and, for a sufficiently massive initial cloud, produce an extremely top-heavy distribution of stellar masses. This potentially repetitive process can therefore explain the presence of multiple eccentric rings of young stars in the presence of a supermassive black hole.