2005/01/11 by Warren R. Brown, Margaret J. Geller, Scott J. Kenyon +1 · 2 citations
Physics and Astronomy · #Astrophysics and Star Formation Studies #Gamma-ray bursts and supernovae #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/429378
published as Astrophys.J. 622 (2005) L33-L36 · 4 pages, submitted to ApJ Letters
arxiv created 2005/01/11 · openalex publication_date 2005/02/21 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
We have discovered a star, SDSS J090745.0+024507, leaving the Galaxy with a heliocentric radial velocity of 853 ± 12 km s -1 , the largest velocity ever observed in the Milky Way halo. The star is either a hot blue horizontal-branch star or a B9 main-sequence star with a heliocentric distance of 39 or 71 kpc, respectively. Corrected for the solar reflex motion and to the local standard of rest, the Galactic rest-frame velocity is 709 km s -1 . We suggest that this star is the first example of a hypervelocity star ejected from the Galactic center, as predicted by Hills and later discussed by Yu & Tremaine. The star's radial velocity vector points 174° from the Galactic center. The star has [Fe/H] ~ 0, consistent with a Galactic center origin, and a travel time of ≲80 Myr from the Galactic center, consistent with its stellar lifetime. If the star is indeed traveling from the Galactic center, it should have a proper motion of ~0.3 mas yr -1 observable with the Space Interferometry Mission or the Global Astrometric Interferometer for Astrophysics . Identifying additional hypervelocity stars throughout the halo will constrain the production rate history of hypervelocity stars at the Galactic center.