The Velocity Distribution of Hypervelocity Stars
- Creators
- Rossi, Elena M.
- Kobayashi, Shiho
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Sari, Re'em
Abstract
We consider the process of stellar binaries tidally disrupted by a supermassive black hole (BH). For highly eccentric orbits, as one star is ejected from the three-body system, the companion remains bound to the BH. Hypervelocity stars (HVSs) observed in the Galactic halo and S-stars observed orbiting the central BH may originate from such mechanism. In this paper, we predict the velocity distribution of the ejected stars of a given mass, after they have traveled out of the Galactic potential. We use both analytical methods and Monte Carlo simulations. We find that each part of the velocity distribution encodes different information. At low velocities <800 km s^(−1), the Galactic potential universally shapes the observed distribution, which rises toward a peak, related to the Galactic escape velocity. Beyond the peak, the velocity distribution depends on binary mass and separation distributions. Finally, the finite star life introduces a break related to their mass. A qualitative comparison of our models with current observations shows the great potential of HVSs to constrain bulge and Galactic properties. Standard choices for parameter distributions predict velocities below and above ~800 km s^(−1) with equal probability, while none are observed beyond ~700 km s^(−1) and the current detections are more clustered at low velocities 300–400 km s^(−1). These features may indicate that the separation distribution of binaries that reach the tidal sphere is not flat in logarithmic space, as observed in more local massive binaries, but has more power toward larger separations, enhancing smaller velocities. In addition, the binary formation/evolution process or the injection mechanism might also induce a cut-off a_min ~ 10 R_☉ in the separation distribution.
Additional Information
© 2014 The American Astronomical Society. Received 2013 July 3; accepted 2014 July 11; published 2014 October 22.Attached Files
Published - 0004-637X_795_2_125.pdf
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Additional details
- Eprint ID
- 52213
- Resolver ID
- CaltechAUTHORS:20141201-101644734
- Created
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2014-12-01Created from EPrint's datestamp field
- Updated
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2021-11-10Created from EPrint's last_modified field