SDSS J090745.0+024507

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SDSS J090745.0+024507
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Hydra
Right ascension 09h 07m 44.99 s
Declination +02° 45′ 06.9″
Spectral type B9
Other designations
SDSS J090744.99+024506.8

SDSS J090744.99+024506.8 (SDSS 090745.0+024507), is a star that is leaving the Milky Way galaxy at twice the galactic escape velocity (0.002 the speed of light). In the past it was a double star system. The other star has fallen into a black hole and this star was greatly accelerated by the black hole. Christened by the astronomer Warren Brown as the Outcast Star, it is the first discovered member of a class of objects named hypervelocity stars.[1]


It was discovered at the MMT Observatory of the Harvard-Smithsonian Center for Astrophysics (CfA), by astronomers Warren Brown, Margaret J. Geller, Scott J. Kenyon and Michael J. Kurtz.[2]

Scientists theorize that the star was ejected out of a binary star system approximately 80 million years ago when it encountered a black hole in the center of the Milky Way galaxy.[citation needed]


The star is about 80 million years old, and as it contains many elements heavier than hydrogen and helium, having formed in the evolved star-forming regions of the galactic core, is considered metal-rich. It is moving directly away from the galactic center at over 1,500,000 miles per hour (2,400,000 km/h), twice as fast as the Milky Way's galactic escape velocity. Eventually the star will leave the galaxy completely.

This scenario was proposed by astronomer Jack G. Hills in 1988, as a possibility for stars encountering a massive black hole.[3]


  1. ^ Berardelli, Phil (February 10, 2005), "In The Stars: Odd Stars, Odder Planets", Space Daily 
  2. ^ Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J. & Kurtz, Michael J. (2005), "Discovery of an Unbound Hypervelocity Star in the Milky Way Halo", Astrophysical Journal 622 (1): L33–L36, arXiv:astro-ph/0501177, Bibcode:2005ApJ...622L..33B, doi:10.1086/429378 
  3. ^ Hills, J. G. (1988), "Hyper-velocity and tidal stars from binaries disrupted by a massive Galactic black hole", Nature 331 (6158): 687–689, Bibcode:1988Natur.331..687H, doi:10.1038/331687a0 

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