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The nature of hypervelocity stars as inferred from their Galactic trajectories

Svensson, Karl M.; Church, Ross P. and Davies, Melvyn B LU (2008) In Monthly Notices of the Royal Astronomical Society 383(1). p.15-19
Abstract
We have computed the Galactic trajectories of 12 hypervelocity stars (HVSs) under the assumption that they originated in the Galactic Centre. We show that eight of these 12 stars are bound to the Galaxy. We consider the subsequent trajectories of the bound stars to compute their characteristic orbital period, which is 2 Gyr. All eight bound stars are moving away from the centre of the Galaxy, which implies that the stars' lifetimes are less than 2 Gyr. We thus infer that the observed HVSs are massive main-sequence stars, rather than blue horizontal branch stars. The observations suggest that blue HVSs are ejected from the Galactic Centre roughly every 15 Myr. This is consistent with the observed population of blue stars in extremely tight... (More)
We have computed the Galactic trajectories of 12 hypervelocity stars (HVSs) under the assumption that they originated in the Galactic Centre. We show that eight of these 12 stars are bound to the Galaxy. We consider the subsequent trajectories of the bound stars to compute their characteristic orbital period, which is 2 Gyr. All eight bound stars are moving away from the centre of the Galaxy, which implies that the stars' lifetimes are less than 2 Gyr. We thus infer that the observed HVSs are massive main-sequence stars, rather than blue horizontal branch stars. The observations suggest that blue HVSs are ejected from the Galactic Centre roughly every 15 Myr. This is consistent with the observed population of blue stars in extremely tight orbits round the central supermassive black hole (SMBH), the so-called S-stars, if we assume that the HVSs are produced by the breakup of binaries. One of the stars in such a binary is ejected at high velocities to form a HVS; the other remains bound to the SMBH as an S-star.



We further show that the one high-velocity system observed to be moving towards the Galactic Centre, SDSS J172226.55+594155.9, could not have originated in the Galactic Centre; rather, we identify it as a halo object. (Less)
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type
Contribution to journal
publication status
published
subject
in
Monthly Notices of the Royal Astronomical Society
volume
383
issue
1
pages
15 - 19
publisher
Wiley-Blackwell
external identifiers
  • wos:000251813700004
  • scopus:46249113696
ISSN
1365-2966
DOI
10.1111/j.1745-3933.2007.00400.x
language
English
LU publication?
yes
id
57c366e7-8c71-4b22-bdf8-ada5be02f57f (old id 772071)
date added to LUP
2007-12-18 17:10:55
date last changed
2017-05-21 03:42:27
@article{57c366e7-8c71-4b22-bdf8-ada5be02f57f,
  abstract     = {We have computed the Galactic trajectories of 12 hypervelocity stars (HVSs) under the assumption that they originated in the Galactic Centre. We show that eight of these 12 stars are bound to the Galaxy. We consider the subsequent trajectories of the bound stars to compute their characteristic orbital period, which is 2 Gyr. All eight bound stars are moving away from the centre of the Galaxy, which implies that the stars' lifetimes are less than 2 Gyr. We thus infer that the observed HVSs are massive main-sequence stars, rather than blue horizontal branch stars. The observations suggest that blue HVSs are ejected from the Galactic Centre roughly every 15 Myr. This is consistent with the observed population of blue stars in extremely tight orbits round the central supermassive black hole (SMBH), the so-called S-stars, if we assume that the HVSs are produced by the breakup of binaries. One of the stars in such a binary is ejected at high velocities to form a HVS; the other remains bound to the SMBH as an S-star.<br/><br>
<br/><br>
We further show that the one high-velocity system observed to be moving towards the Galactic Centre, SDSS J172226.55+594155.9, could not have originated in the Galactic Centre; rather, we identify it as a halo object.},
  author       = {Svensson, Karl M. and Church, Ross P. and Davies, Melvyn B},
  issn         = {1365-2966},
  language     = {eng},
  number       = {1},
  pages        = {15--19},
  publisher    = {Wiley-Blackwell},
  series       = {Monthly Notices of the Royal Astronomical Society},
  title        = {The nature of hypervelocity stars as inferred from their Galactic trajectories},
  url          = {http://dx.doi.org/10.1111/j.1745-3933.2007.00400.x},
  volume       = {383},
  year         = {2008},
}