Intermediate-mass runaway and hypervelocity star candidates in DESI DR1
Abstract
Runaway stars ejected from the Galactic disc span a range of velocities, with two extreme regimes of particular interest. Hyper-runaway stars reach velocities approaching the local Galactic escape speed while remaining gravitationally bound to the Galaxy, while hypervelocity stars (HVS) have speeds which exceed the escape speed, leaving them formally unbound. Studying both populations places stringent constraints on star cluster formation, supernova explosions in massive binaries, and the shape of the stellar halo. Here we present a spectroscopic search for such extreme-velocity stars using data from the first data release of the Dark Energy Spectroscopic Instrument (DESI DR1). Because these objects are typically located at distances beyond the range where \textit{gaia} parallaxes are reliable, we derive stellar parameters through a combined analysis of spectroscopy and spectral energy distributions (SEDs). These parameters are then compared with stellar evolutionary tracks to infer distances, which are subsequently used to compute the kinematics of the candidates. We identify a sub-sample of eight stars that appear unbound to the Galaxy, likely of extragalactic origin. These stars exhibit projected rotational velocities exceeding $50$ km s−1, consistent with a main-sequence nature. An additional eleven stars are identified as potential HVS candidates under the assumption that they are main-sequence stars. This interpretation is not supported by their rotational velocities, making their unbound status less secure. Finally, $26$ stars show evidence of being main-sequence runaway stars ejected from the Galactic disc. The fastest object in the sample is a metal-poor HVS candidate with a Galactocentric velocity upper-limit of 934 ± 110 km s−1. The star with the largest measured radial velocity of $513$ km s−1 is most likely a slowly pulsating B-type runaway star.
Related
- FROST-CLUSTERS – III. Metallicity-dependent intermediate-mass black hole formation by runaway collisions in dense star clusters
- From Dense Gas Clouds to Supermassive Black Hole Seeds: Hybrid Hydro/Direct N-body Simulations of Runaway Collision-driven Intermediate-mass Black Hole Formation
- Pebbles to Gems: Intermediate-mass black holes in the first star clusters
- Constraints on the Intranight Optical Variability of Intermediate-Mass Black Hole Candidates
- Uncovering the Origin of Slow Rotators among Intermediate-Mass Stars in the Star-Forming Cluster Trumpler 14
BibTeX
@misc{bhat2026intermediatemass,
title = {{Intermediate-mass runaway and hypervelocity star candidates in DESI DR1}},
author = {Aakash Bhat and Matti Dorsch and Ulrich Heber and Stephan Geier and Harry Dawson},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2608.30063},
eprint = {2608.30063},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.30063},
}
RIS
TY - UNPB
TI - Intermediate-mass runaway and hypervelocity star candidates in DESI DR1
AU - Aakash Bhat
AU - Matti Dorsch
AU - Ulrich Heber
AU - Stephan Geier
AU - Harry Dawson
PY - 2026
DA - 2026/08/30
PB - arXiv
DO - 10.48550/arxiv.2608.30063
UR - https://arxiv.org/abs/2608.30063
AB - Runaway stars ejected from the Galactic disc span a range of velocities, with two extreme regimes of particular interest. Hyper-runaway stars reach velocities approaching the local Galactic escape speed while remaining gravitationally bound to the Galaxy, while hypervelocity stars (HVS) have speeds which exceed the escape speed, leaving them formally unbound. Studying both populations places stringent constraints on star cluster formation, supernova explosions in massive binaries, and the shape of the stellar halo. Here we present a spectroscopic search for such extreme-velocity stars using data from the first data release of the Dark Energy Spectroscopic Instrument (DESI DR1). Because these objects are typically located at distances beyond the range where \textit{gaia} parallaxes are reliable, we derive stellar parameters through a combined analysis of spectroscopy and spectral energy distributions (SEDs). These parameters are then compared with stellar evolutionary tracks to infer distances, which are subsequently used to compute the kinematics of the candidates. We identify a sub-sample of eight stars that appear unbound to the Galaxy, likely of extragalactic origin. These stars exhibit projected rotational velocities exceeding $50$ km s^−1, consistent with a main-sequence nature. An additional eleven stars are identified as potential HVS candidates under the assumption that they are main-sequence stars. This interpretation is not supported by their rotational velocities, making their unbound status less secure. Finally, $26$ stars show evidence of being main-sequence runaway stars ejected from the Galactic disc. The fastest object in the sample is a metal-poor HVS candidate with a Galactocentric velocity upper-limit of 934 ± 110 km s^−1. The star with the largest measured radial velocity of $513$ km s^−1 is most likely a slowly pulsating B-type runaway star.
ER -