Hypervelocity Stars III. The Space Density and Ejection History of Main Sequence Stars from the Galactic Center

Abstract

We report the discovery of 3 new unbound hypervelocity stars (HVSs), stars traveling with such extreme velocities that dynamical ejection from a massive black hole (MBH) is their only suggested origin. We also detect a population of possibly bound HVSs. The significant asymmetry we observe in the velocity distribution -- we find 26 stars with v_rf > 275 km/s and 1 star with v_rf < -275 km/s -- shows that the HVSs must be short-lived, probably 3 - 4 Msun main sequence stars. Any population of hypervelocity post-main sequence stars should contain stars falling back onto the Galaxy, contrary to the observations. The spatial distribution of HVSs also supports the main sequence interpretation: longer-lived 3 Msun HVSs fill our survey volume; shorter-lived 4 Msun HVSs are missing at faint magnitudes. We infer that there are 96 +- 10 HVSs of mass 3 - 4 Msun within R < 100 kpc, possibly enough HVSs to constrain ejection mechanisms and potential models. Depending on the mass function of HVSs, we predict that SEGUE may find up to 5 - 15 new HVSs. The travel times of our HVSs favor a continuous ejection process, although a ~120 Myr-old burst of HVSs is also allowed.

10 pages, 8 figures, accepted to ApJ, minor revisions

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Cited by in corpus (15)

• Deep MMT Transit Survey of the Open Cluster M37 II: Variable Stars
• Kinematics of the old stellar population at the Galactic Center
• An Alternative Origin for Hypervelocity Stars
• Milky Way potentials in CDM and MOND. Is the Large Magellanic Cloud on a bound orbit?
• Runaway and hypervelocity stars in the Galactic halo: Binary rejuvenation and triple disruption
• Binary dynamics near a massive black hole
• Dynamical and evolutionary constraints on the nature and origin of hypervelocity stars
• LMC origin of the hyper-velocity star HE 0437-5439. Beyond the supermassive black hole paradigm
• The Anisotropic Spatial Distribution of Hypervelocity Stars
• Hypervelocity Stars from the Andromeda Galaxy
• HVS7: a chemically peculiar hyper-velocity star
• Low Metallicity Indicates that the Hypervelocity Star HE 0437-5439 was Ejected from the LMC
• 'Slow' and Fast Rotators among Hypervelocity Stars
• Hypervelocity Stars: Young and Heavy or Old and Light?
• Extreme Horizontal Branch Stars