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Hypervelocity Stars Ejected from the Galactic Center

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. Radial Velocities from the MMT. The first “Hypervelocity Star”. Predictions. NY Times

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Hypervelocity Stars Ejected from the Galactic Center

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  1. Hypervelocity StarsEjected 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 NY Times 2/22/2005 Hills, 1988, Nature: prediction Hills, 1991, AJ: orbits Yu & Tremaine, 2003, ApJ: rates “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 Brown et al. (2005) • B9 main sequence star. • Solar metallicity. • g=19.8 thus d=110 kpc. • Travel time ~160 Myr.

  10. Our Search for more Hypervelocity Stars O B F A G K M Fukugita et al (1996) Brown et al. (2006a, 2006b, 2007a, 2007b)

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

  12. Radial Velocities HVSs Brown et al (2007b)

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

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

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

  16. HVS: Sky Distribution +90 60 30 120 240 300 360 180 0 60 -30 -60 -90 Brown et al. (2007a) - 300 0 +300 km/s

  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 LISA Ginsburg & Loeb (2006)

  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 a unique window on the Galactic Center: • Mass function of stars • In-fall history • Massive black hole (binary?) NY Times

  21. The Hypervelocity Stars

  22. Mass Function of Stars We Observe: 7 HVS in 6000 deg2 ~50 3-4 Msun HVSs Salpeter 16 3-4 Msun stars Predicted: 2000 HVSs (Yu & Tremaine) Arches ~100 3-4 Msun stars NASA HST

  23. Halo Structure: Sgr Stream

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