Discovery of Galactic-centre-ejected star in DESI DR1

Astronomy and Astrophysics, vol. 709, pp. A117

Abstract

Hypervelocity stars (HVSs) are stars ejected from the Galactic centre (GC) through tidal interactions with the central supermassive black hole. Formed in the immediate vicinity of Sgr A * , these stars are accelerated to velocities high enough to escape the GC and be observable in the Galactic halo. Using spectroscopy from the Dark Energy Spectroscopic Instrument (DESI) and astrometry from Gaia , we conducted a six-dimensional search for HVSs and identified a compelling candidate, hereafter called DESI-312, whose bound trajectory can be confidently traced back to the central 2 kpc of our galaxy. The star resides in the inner halo and exhibits supersolar metallicity ( [Fe/H] = 0.27 ± 0.09), which makes it distinct from other known stellar populations with radial orbits. Its inferred GC ejection velocity of 698-27 is consistent with a Hills mechanism ejection, and suggests its origin lies in the innermost regions of the Milky Way. We considered alternative origins for the star, including disc ejections from young clusters and globular clusters, but these scenarios fail to explain both its orbit and metallicity. Unlike previously identified A- and B-type HVSs, DESI-312 is a ∼1 M ⊙ star on the main sequence or early sub-giant branch, which enables a detailed chemical analysis of its atmosphere and offers a rare window -unobscured by dust and crowding - into the composition of the central regions of the Galaxy.

Authors 5

1. Manuel Cavieres Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University

2. Sergey E. Koposov

   University of Cambridge · Royal Observatory · University of Edinburgh

   Affiliation as printed

   Institute for Astronomy, University of Edinburgh, Royal Observatory

   Institute of Astronomy, University of Cambridge

3. Elena Maria Rossi Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University

4. Zephyr Penoyre Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University

5. Sill Verberne Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University