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Photograph of Ross Church

Ross Church

Senior lecturer

Photograph of Ross Church

Close encounters involving free-floating planets in star clusters

Author

  • Long Wang
  • M. B. N. Kouwenhoven
  • Xiaochen Zheng
  • Ross Church
  • Melvyn B Davies

Summary, in English

Instabilities in planetary systems can result in the ejection of planets from their host system, resulting in free-floating planets (FFPs). If this occurs in a star cluster, the FFP may remain bound to the star cluster for some time and interact with the other cluster members until it is ejected. Here, we use N-body simulations to characterize close star-planet and planet-planet encounters and the dynamical fate of the FFP population in star clusters containing 500-2000 single or binary star members. We find that FFPs ejected from their planetary system at low velocities typically leave the star cluster 40 per cent earlier than their host stars, and experience tens of close (< 1000 au) encounters with other stars and planets before they escape. The fraction of FFPs that experiences a close encounter depends on both the stellar density and the initial velocity distribution of the FFPs. Approximately half of the close encounters occur within the first 30 Myr, and only 10 per cent occur after 100 Myr. The periastron velocity distribution for all encounters is well described by a modified Maxwell-Bolzmann distribution, and the periastron distance distribution is linear over almost the entire range of distances considered, and flattens off for very close encounters due to strong gravitational focusing. Close encounters with FFPs can perturb existing planetary systems and their debris structures, and they can result in re-capture of FFPs. In addition, these FFP populations may be observed in young star clusters in imaging surveys; a comparison between observations and dynamical predictions may provide clues to the early phases of stellar and planetary dynamics in star clusters.

Department/s

  • Lund Observatory

Publishing year

2015

Language

English

Pages

3543-3558

Publication/Series

Monthly Notices of the Royal Astronomical Society

Volume

449

Issue

4

Document type

Journal article

Publisher

Oxford University Press

Topic

  • Astronomy, Astrophysics and Cosmology

Keywords

  • planets and satellites: dynamical evolution and stability
  • stars:
  • kinematics and dynamics
  • open clusters and associations: general

Status

Published

ISBN/ISSN/Other

  • ISSN: 1365-2966