# New nearby hypervelocity stars and their spatial distribution from Gaia DR2

## TL;DR

This study identifies over 600 high-velocity stars, including 28 nearby hypervelocity stars, using Gaia DR2 data, and analyzes their spatial distribution revealing significant anisotropy linked to their origins.

## Contribution

The paper presents a new method to identify hypervelocity stars from Gaia DR2 data and reports the discovery of 28 nearby hypervelocity stars with high unbound probabilities.

## Key findings

- Unbound hypervelocity stars are spatially anisotropic, especially in Galactic longitude.
- 12 of the identified hypervelocity stars are previously reported by other surveys.
- Lower unbound probability HVSs tend to be more isotropically distributed.

## Abstract

Base on about 4,500 large tangential velocity ($V_\mathrm{tan}>0.75V_\mathrm{esc}$) with high-precision proper motions and $5\sigma$ parallaxes in Gaia DR2 5D information derived from parallax and proper motion, we identify more than 600 high velocity stars with $50\%$ unbound probability. Of these, 28 nearby (less than 6 kpc) late-type Hypervelocity stars (HVSs) with over $99\%$ possibility of unbound are discovered. In order to search for the unbound stars from the full Gaia DR2 6D phase space information derived from parallax, proper motion and radial velocity, we also identify 28 stars from the total velocity ($V_\mathrm{gc}>0.75V_\mathrm{esc}$) that have probabilities greater than $50\%$ of being unbound from the Galaxy. Of these, only three have a nearly $99\%$ probabilities of being unbound. On the whole HVSs subsample, there is 12 sources reported by other surveys. We study the spatial distribution of angular positions and angular separation of HVSs. We find the unbound HVSs are spatially anisotropic that is most significant in the Galactic longitude at more than $3\sigma$ level, and lower unbound probability HVSs are systematically more isotropic. The spatial distribution can reflect the origin of HVSs and we discuss the possible origin link with the anisotropy.