Forming isolated brown dwarfs by turbulent fragmentation

Lomax, O.; Whitworth, A. P. und Hubber, D. A. (2016): Forming isolated brown dwarfs by turbulent fragmentation. In: Monthly Notices of the Royal Astronomical Society, Bd. 458, Nr. 2: S. 1242-1252

Abstract

We use Smoothed Particle Hydrodynamics to explore the circumstances under which an isolated very low mass pre-stellar core can be formed by colliding turbulent flows and collapse to form a brown dwarf. Our simulations suggest that the flows need not be very fast, but do need to be very strongly convergent, i.e. the gas must flow in at comparable speeds from all sides, which seems rather unlikely. We therefore revisit the object Oph-B11, which Andr, et al. have identified as a pre-stellar core with mass between similar to 0.020 M-aS (TM) and similar to 0.030 M-aS (TM). We re-analyse the observations using a Markov-chain Monte Carlo method that allows us (i) to include the uncertainties on the distance, temperature and dust mass opacity, and (ii) to consider different Bayesian prior distributions of the mass. We estimate that the posterior probability that Oph-B11 has a mass below the hydrogen-burning limit at similar to 0.075 M-aS (TM), is between 0.66 and 0.86 . We conclude that, if Oph-B11 is destined to collapse, it probably will form a brown dwarf. However, the flows required to trigger this appear to be so contrived that it is difficult to envisage this being the only way, or even a major way, of forming isolated brown dwarfs. Moreover, Oph-B11 could easily be a transient, bouncing, prolate core, seen end-on;there could, indeed should, be many such objects masquerading as very low mass pre-stellar cores.

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Physik
• Themengebiete: 500 Naturwissenschaften und Mathematik > 530 Physik
• ISSN: 0035-8711
• Sprache: Englisch