The Galactic Distribution of Fragments Formed from Tidally Disrupted Stars

TL;DR

This paper models the formation and distribution of planetary-mass fragments resulting from tidally disrupted stars near the Milky Way's supermassive black hole, predicting their numbers, velocities, and locations within and outside our galaxy.

Contribution

It introduces a detailed phase space analysis of fragments from stellar disruptions by Sgr A*, including their expected distribution and velocities in the galaxy.

Findings

Approximately 10^7 fragments from Sgr A* are in the Milky Way.

About 10^7 fragments from other galaxies are within 1 Mpc.

The nearest fragment to the Sun is typically 500 pc away.

Abstract

Approximately once every $10^4$ years, a star passes close enough to the supermassive black hole Sgr A* at the center of the Milky Way to be pulled apart by the black hole's tidal forces. The star is then "spaghettified" into a long stream of matter, with approximately one half being bound to Sgr A* and the other half unbound. Within this stream, the local self-gravity dominates the tidal field of Sgr A*, which at minimum restricts the stream to a small finite width. As the stream cools from adiabatic expansion and begins to recombine, the residual self-gravity allows for planetary-mass fragments to form along the length of the stream; these fragments are then shot out into the galaxy at range of velocities, with the fastest moving at ~10% c. We determine the phase space distributions of these fragments for a realistic ensemble of stellar disruptions, along with the local density of fragments in the solar neighborhood. We find that ~$10^7$ fragments produced by Sgr A* accumulate within the Milky Way over its lifetime, that there are ~$10^7$ fragments that lie within 1 Mpc of the Milky Way originating from other galaxies, and that the nearest fragment to our Sun is on average 500 pc distant.