Runaway and hypervelocity stars. The supernova connection

TL;DR

This paper investigates the origins of runaway and hypervelocity stars, comparing their observed velocities with theoretical models, and suggests a variant of the binary ejection mechanism to explain the fastest stars that can escape the galaxy.

Contribution

It provides a detailed analysis of the velocity distribution of runaway stars and introduces a modified binary ejection mechanism to account for hypervelocity stars beyond standard predictions.

Findings

Most runaway stars are explained by standard ejection mechanisms.

A subset of stars exceeds predicted velocities, suggesting a variant of the BEM.

Hypervelocity stars can be produced by this modified mechanism.

Abstract

We present an investigation of the known sample of runaway stars. The orbits of these stars are traced back to their origin in the Galactic disc. The velocity distribution of these stars is compared to theoretical predictions. We conclude that the majority of stars is well explained by the standard binary ejection mechanism (BEM) and the dynamical ejection mechanism (DEM). However, we find a sample of ten stars which has ejection velocities in excess of those predicted by standard scenarios. We discuss how these can be explained by a variant of the BEM. This mechanism can create runaway stars exceeding the Galactic escape velocity (known as hypervelocity stars). The number of runaway stars in our Galaxy is estimated and compared to the known sample of high mass X-ray binaries, whose formation is linked to the BEM channel.