# Formation and spatial distribution of hypervelocity stars in AGN outflows

## TL;DR

This paper explores how star formation within AGN-driven outflows can produce hypervelocity stars, revealing a potentially dominant mechanism for their creation and predicting their spatial distribution for future observations.

## Contribution

It demonstrates that cold clumps formed in AGN outflows can generate hypervelocity stars at a much higher rate than previous mechanisms, providing new insights into their origins.

## Key findings

- Cold clumps of ~10^3 solar masses form within 10^5 years in AGN outflows.
- Star formation rate in outflows is 4-5 orders of magnitude higher than previous mechanisms.
- Hypervelocity stars are produced along outflow paths and can escape into intergalactic space.

## Abstract

We study star formation within outflows driven by active galactic nuclei (AGN) as a new source of hypervelocity stars (HVSs). Recent observations revealed active star formation inside a galactic outflow at a rate of $\sim 15\,M_{\odot}\,\rm yr^{-1}$. We verify that the shells swept up by an AGN outflow are capable of cooling and fragmentation into cold clumps embedded in a hot tenuous gas via thermal instabilities. We show that cold clumps of $\sim 10^3\,M_{\odot}$ are formed within $\sim 10^5$ yrs. As a result, stars are produced along outflow's path, endowed with the outflow speed at their formation site. These HVSs travel through the galactic halo and eventually escape into the intergalactic medium. The expected instantaneous rate of star formation inside the outflow is $\sim 4-5$ orders of magnitude greater than the average rate associated with previously proposed mechanisms for producing HVSs, such as the Hills mechanism and three-body interaction between a star and a black hole binary. We predict the spatial distribution of HVSs formed in AGN outflows for future observational probe.