An Old, Low-mass, Metal-poor Hypervelocity Star Candidate Consistent with a Galactic Center Origin

The Astrophysical Journal Letters, vol. 1003, pp. L9

Abstract

Abstract We report the discovery of DESI-HVS1, a hypervelocity star (HVS) candidate identified from DESI DR1 spectroscopy and Gaia DR3 astrometry. DESI-HVS1 is an old, low-mass, metal-poor F-type star with a mass of 0.8 M ⊙ , an age of ∼14.1 Gyr, and [Fe/H] = −1.6. It is located at a heliocentric distance of 3.7 7 − 0.36 + 0.39 kpc and has a Galactocentric total velocity of 52 3 − 47 + 46 km s − 1 , marginally exceeding the local escape speed, corresponding to an unbound probability of P ub ∼ 50%. Backward orbit integrations show that DESI-HVS1 had the closest approach to the Galactic center (GC) of 0.4 0 − 0.11 + 0.23 kpc , with a velocity of 68 2 − 35 + 22 km s − 1 and a flight time of 12.8 9 − 0.74 + 0.92 Myr . The reconstructed orbit exhibits a clear perigalactic turning point and only a single crossing of the Galactic midplane ( P cross > 0.95). These properties suggest that DESI-HVS1 is most naturally explained by the Hills mechanism, although alternative scenarios cannot be entirely ruled out. Its discovery provides the first strong evidence for an old, low-mass HVS candidate consistent with a GC origin, indicating that the apparent dominance of young, massive GC-origin HVSs is likely a consequence of observational selection effects.

Authors 7

1. Shunhong Deng

   China West Normal University · University of Chinese Academy of Sciences

   Affiliation as printed

   China West Normal University

   University of Chinese Academy of Sciences

2. Y Huang

   Chinese Academy of Sciences · University of Chinese Academy of Sciences

   Affiliation as printed

   Chinese Academy of Sciences

   University of Chinese Academy of Sciences

3. Haozhu Fu

   Peking University

   Affiliation as printed

   Peking University

4. Yongkang Sun

   Chinese Academy of Sciences · University of Chinese Academy of Sciences

   Affiliation as printed

   Chinese Academy of Sciences

   University of Chinese Academy of Sciences

5. Qikang Feng

   Peking University

   Affiliation as printed

   Peking University

6. Guoyang Chen Aachen

   Leiden University · Chinese Academy of Sciences

   Affiliation as printed

   Chinese Academy of Sciences

   Leiden University

7. Hailong Zhang

   Peking University

   Affiliation as printed

   Peking University