Induced metal-free star formation around a massive black hole seed

TL;DR

This study explores how a massive black hole seed influences its host halo, leading to metal-free star formation triggered by X-ray ionization and heating, resulting in a compact stellar cluster that is later quenched by supernova feedback.

Contribution

It demonstrates the process of metal-free star formation induced by black hole X-ray radiation and its impact on early galaxy evolution.

Findings

X-ray radiation ionizes and heats the medium, promoting H2 formation.

A ~10^4 solar mass metal-free stellar cluster forms within a million years.

Supernova feedback quenches further star formation for tens of millions of years.

Abstract

The direct formation of a massive black hole is a potential seeding mechanism of the earliest observed supermassive black holes. We investigate how the existence of a massive black hole seed impacts the ionization and thermal state of its pre-galactic host halo and subsequent star formation. We show that its X-ray radiation ionizes and heats the medium, enhancing $\rm{H}_2$ formation in shielded regions, within the nuclear region in the span of a million years. The enhanced molecular cooling triggers the formation of a $\sim 10^4~{\rm M}_\odot$ metal-free stellar cluster at a star formation efficiency of $\sim 0.1\%$ in a single event. Star formation occurs near the edges of the H II region that is partially ionized by X-rays, thus the initial size depends on the black hole properties and surrounding environment. The simulated metal-free galaxy has an initial half-light radius of $\sim 10$ pc but expands to $\sim 50$ pc after 10 million years because of the outward velocities of their birth clouds. Supernova feedback then quenches any further star formation for tens of millions of years, allowing the massive black hole to dominate the spectrum once the massive metal-free stars die.