Substellar companions and isolated planetary-mass objects from protostellar disc fragmentation

W. K. M. Rice, P. J. Armitage, I. A. Bonnell, M. R. Bate, S. V. Jeffers, S. G. Vine

Research output: Contribution to journalArticlepeer-review

Abstract

Self-gravitating protostellar discs are unstable to fragmentation if the gas can cool on a time-scale that is short compared with the orbital period. We use a combination of hydrodynamic simulations and N-body orbit integrations to study the long-term evolution of a fragmenting disc with an initial mass ratio to the star of Mdisc/M*= 0.1. For a disc that is initially unstable across a range of radii, a combination of collapse and subsequent accretion yields substellar objects with a spectrum of masses extending (for a Solar-mass star) up to ~0.01 Msolar. Subsequent gravitational evolution ejects most of the lower mass objects within a few million years, leaving a small number of very massive planets or brown dwarfs in eccentric orbits at moderately small radii. Based on these results, systems such as HD 168443 - in which the companions are close to or beyond the deuterium burning limit - appear to be the best candidates to have formed via gravitational instability. If massive substellar companions originate from disc fragmentation, while lower-mass planetary companions originate from core accretion, the metallicity distribution of stars which host massive substellar companions at radii of ~1 au should differ from that of stars with lower mass planetary companions.
Original languageEnglish
JournalMonthly Notices of the Royal Astronomical Society
Volume346
Publication statusPublished - 1 Dec 2003

Keywords

  • accretion
  • accretion discs
  • planets and satellites: formation
  • stars: low-mass
  • brown dwarfs
  • planetary systems: protoplanetary discs
  • stars: pre-main sequence

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