{
  "id": "1206.4057",
  "version": "v1",
  "published": "2012-06-18T20:00:59.000Z",
  "updated": "2012-06-18T20:00:59.000Z",
  "title": "The Nature of Hypervelocity Stars and the Time Between Their Formation and Ejection",
  "authors": [
    "Warren R. Brown",
    "Judith G. Cohen",
    "Margaret J. Geller",
    "Scott J. Kenyon"
  ],
  "comment": "6 pages, accepted to ApJ Letters",
  "categories": [
    "astro-ph.GA",
    "astro-ph.SR"
  ],
  "abstract": "We obtain Keck HIRES spectroscopy of HVS5, one of the fastest unbound stars in the Milky Way halo. We show that HVS5 is a 3.62 +- 0.11 Msun main sequence B star at a distance of 50 +- 5 kpc. The difference between its age and its flight time from the Galactic center is 105 +-18(stat)+-30(sys) Myr; flight times from locations elsewhere in the Galactic disk are similar. This 10^8 yr `arrival time' between formation and ejection is difficult to reconcile with any ejection scenario involving massive stars that live for only 10^7 yr. For comparison, we derive arrival times of 10^7 yr for two unbound runaway B stars, consistent with their disk origin where ejection results from a supernova in a binary system or dynamical interactions between massive stars in a dense star cluster. For HVS5, ejection during the first 10^7 yr of its lifetime is ruled out at the 3-sigma level. Together with the 10^8 yr arrival times inferred for three other well-studied hypervelocity stars (HVSs), these results are consistent with a Galactic center origin for the HVSs. If the HVSs were indeed ejected by the central black hole, then the Galactic center was forming stars ~200 Myr ago, and the progenitors of the HVSs took ~100 Myr to enter the black hole's loss cone.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2012-06-18T20:00:59.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "hypervelocity stars",
      "flight time",
      "black holes loss cone",
      "yr arrival times",
      "msun main sequence"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1088/2041-8205/754/1/L2",
      "journal": "The Astrophysical Journal",
      "year": 2012,
      "month": "Jul",
      "volume": 754,
      "number": 1
    },
    "note": {
      "typesetting": "TeX",
      "pages": 6,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1118684,
      "adsabs": "2012ApJ...754L...2B"
    }
  }
}