1. Hypervelocity Stars Ejected from the Galactic Center STScI Colloquium Oct 3, 2007 Warren R. Brown Smithsonian Astrophysical Observatory Collaborators: Margaret Geller, Scott Kenyon, Michael Kurtz

2. Radial Velocities from the MMT

3. The first “Hypervelocity Star”

4. Predictions Hills, 1988, Nature: prediction Hills, 1991, AJ: orbits Yu & Tremaine, 2003, ApJ: rates NY Times 2/22/2005 “It’s high time someone found it.” - Jack Hills SF Chronicle, 2/11/2005

5. The Milky Way Kaufmann

6. The Galactic Center http://www.mpe.mpg.de/ir/GC/prop.html

7. Eisenhauer et al. 2003

8. Three-body exchange Bromley 2005

9. An Unexpected Star B9 main sequence star. Solar metallicity. g=19.8 thus d=110 kpc. Travel time ~160 Myr. Brown et al. (2005)

10. Our Search for more Hypervelocity Stars Fukugita et al (1996) Brown et al. (2006a, 2006b, 2007a, 2007b)

11. Lowest Mass White Dwarf Kilic et al (2007a,b) Extremely Metal Poor Galaxy Kewley et al. (2007) Brown et al. (2007c) log(O/H)+12 = 7.44 Spectroscopic Observations of an Unusual Parameter Space

12. Radial Velocities Brown et al (2007b)

13. HVS: Ejection Model Bromley et al (2006); Brown et al. (2007a)

14. HVS: Main Sequence Stars Brown et al. (2007b) Blue HB MS Kaufmann Horizontal Branch HVSs

15. HVS: Locations and Travel Times Brown et al. (2007b)

16. - 300 0 +300 km/s HVS: Sky Distribution Brown et al. (2007a) +90 60 30 0 -60 -30 -90 120 60 180 240300360

17. HVS: Space Density Brown et al. (2007b)

18. Theoretical Applications Dark Matter Potential: Gnedin et al (2005), Yu & Madau (2007) Binary Black Hole / origin: Baumgardt et al, Gualandris et al, Merritt, Levin, O’Leary & Loeb, Perets et al, Sesana et al., Lu et al., Svensson et al. Stars orbiting the BH: Ginsburg & Loeb Stellar Populations: Demarque & Virani, Kollmeier & Gould Ginsburg & Loeb (2006) LISA

19. Future Work Discovery survey: MMT, Whipple 1.5m. Spectroscopic identifications: VLT (Heber), WHT (Keenan). Space velocities: HST (Gnedin). Variability: MDM (Stanek). Numerical simulations: (Bromley). Unusual objects: more to come!

20. Conclusions MBH = hypervelocity stars. First HVS: B star +850 km/s. Now 10 known HVSs. HVSs  unique window on the Galactic Center: Mass function of stars In-fall history Massive black hole (binary?) NY Times

21. The Hypervelocity Stars IDTypeg’ (mag) V minRF (km/s) d (kpc) t GC (Myr) Citation HVS1B19.8+709110160 Brown et al. (2005) HVS2sdO18.8+7171932 Hirsch et al. (2005) HVS3B16.2+54861100? Edelmann et al. (2005) HVS4B18.4+55875140 Brown et al. (2006a) HVS5B17.9+6385590 Brown et al. (2006a) HVS6B19.1+50875160 Brown et al. (2006b) HVS7B17.7+42355120 Brown et al. (2006b) HVS8B17.9+43045100 new! HVS9B18.6+49055110 new! HVS10B19.2+43285190 new!

22. Mass Function of Stars Arches Predicted: 2000 HVSs (Yu & Tremaine) We Observe: 7 HVS in 6000 deg 2 ~50 3-4 M sun HVSs 16 3-4 M sun stars ~100 3-4 M sun stars NASA HST Salpeter

23. Halo Structure: Sgr Stream