Sgr A$^*$ envelope explosion and the young stars in the centre of the Milky Way

TL;DR

This paper proposes that the young stars near Sgr A* formed from a massive gas shell expelled by the black hole's energetic outflow, explaining their properties and orbits.

Contribution

It introduces a novel hypothesis that young stars in the Galactic center originated from a black hole-driven gas shell, a process involving extreme outflows and atomic hydrogen formation.

Findings

A massive gas shell (>10^5 solar masses) can produce the observed young stars.

Black hole outflows must be highly super-Eddington for a brief period.

Stars may have formed from atomic hydrogen due to extreme pressure.

Abstract

Sgr A$^*$ is the super massive black hole residing in the centre of the Milky Way. There is plenty of observational evidence that a massive gas cloud fell into the central parsec of the Milky Way $\sim 6$ million years ago, triggering formation of a disc of young stars and activating Sgr A$^*$. In addition to the disc, there is an unexplained population of young stars on randomly oriented orbits. Here we hypothesize that these young stars were formed by fragmentation of a massive quasi-spherical gas shell driven out from Sgr A$^*$ potential well by an energetic outflow. To account for the properties of the observed stars, the shell must be more massive than $10^5$ Solar masses, be launched from inside $\sim 0.01$~pc, and the feedback outflow has to be highly super-Eddington albeit for a brief period of time, producing kinetic energy of at least $10^{55}$~erg. The young stars in the central parsec of the Galaxy may be a unique example of stars formed from atomic rather than molecular hydrogen, and forged by extreme pressure of black hole outflows.