Tidally induced brown dwarf and planet formation in circumstellar discs

Abstract

Most stars are born in clusters and the resulting gravitational interactions between cluster members may significantly affect the evolution of circumstellar discs and therefore the formation of planets and brown dwarfs. Recent findings suggest that tidal perturbations of typical circumstellar discs due to close encounters may inhibit rather than trigger disc fragmentation and so would seem to rule out planet formation by external tidal stimuli. However, the disc models in these calculations were restricted to disc radii of 40 AU and disc masses below 0.1 M_sun. Here we show that even modest encounters can trigger fragmentation around 100 AU in the sorts of massive (~0.5 M_sun), extended (>=100 AU) discs that are observed around young stars. Tidal perturbation alone can do this, no disc-disc collision is required. We also show that very-low-mass binary systems can form through the interaction of objects in the disc. In our computations, otherwise non-fragmenting massive discs, once perturbed, fragment into several objects between about 0.01 and 0.1 M_sun, i.e., over the whole brown dwarf mass range. Typically these orbit on highly eccentric orbits or are even ejected. While probably not suitable for the formation of Jupiter- or Neptune-type planets, our scenario provides a possible formation mechanism for brown dwarfs and very massive planets which, interestingly, leads to a mass distribution consistent with the canonical substellar IMF. As a minor outcome, a possible explanation for the origin of misaligned extrasolar planetary systems is discussed.

9 pages, 5 figures, uses emulateapj. Published in ApJ. Minor changes to match published version. For associated media files see http://www.astro.uni-bonn.de/~webaiub/english/downloads.php

References in corpus (12)

• The properties of brown dwarfs and low-mass hydrogen-burning stars formed by disc fragmentation
• Brown dwarf formation by gravitational fragmentation of massive, extended protostellar discs
• The minimum mass for star formation, and the origin of binary brown dwarfs
• Radiative transfer and the energy equation in SPH simulations of star formation
• Can giant planets form by gravitational fragmentation of discs?
• Numerical requirements for simulations of self gravitating and non-self gravitating disks
• Disk Dispersal and Planet Formation Time Scales
• Injection of Short-Lived Radionuclides into the Early Solar System from a Faint Supernova with Mixing-Fallback
• Brown dwarf formation by binary disruption
• A discontinuity in the low-mass IMF - the case of high multiplicity
• Protostellar collapse: A comparison between SPH and AMR calculations
• The role of the energy equation in the fragmentation of protostellar discs during stellar encounters