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Photograph of Ross Church

Ross Church

Senior lecturer

Photograph of Ross Church

The nature of hypervelocity stars as inferred from their Galactic trajectories

Author

  • Karl M. Svensson
  • Ross P. Church
  • Melvyn B Davies

Summary, in English

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.

Department/s

  • Lund Observatory

Publishing year

2008

Language

English

Pages

15-19

Publication/Series

Monthly Notices of the Royal Astronomical Society

Volume

383

Issue

1

Document type

Journal article

Publisher

Oxford University Press

Topic

  • Astronomy, Astrophysics and Cosmology

Status

Published

Research group

  • Observational and Theoretical Astrophysics

ISBN/ISSN/Other

  • ISSN: 1365-2966