Close encounters involving free-floating planets in star clusters

Long Wang*, M. B.N. Kouwenhoven, Xiaochen Zheng, Ross P. Church, Melvyn B. Davies

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

28 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)3543-3558
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Volume449
Issue number4
DOIs
Publication statusPublished - 21 Mar 2015
Externally publishedYes

Keywords

  • Open clusters and associations: general
  • Planets and satellites: dynamical evolution and stability
  • Stars: kinematics and dynamics

Cite this