Formation of free-floating and companion brown dwarfs

Author(s)

Eduard Vorobyov, Shantanu Basu

Abstract

The formation of brown dwarfs (BDs) is usually attributed to either of two distinct
mechanisms: the direct collapse of a cloud core whose mass straddles the substellar mass limit and gravitational fragmentation in dense filaments and/or
circumstellar disks, often followed by ejection of sub-stellar objects from their
birth sites. It is likely that both mechanisms coexist and complement each other.
However, an important argument usually in favor of the direct collapse scenario
is the observation of some very-low-mass isolated proto-BD clumps, which,
until recently, were dicult to explain by gravitational fragmentation. In this
article, we will review the latest developments in the gravitational fragmentation
scenario of BD formation. Disk fragmentation models that allow ejection of gaseous proto-BDs (and not only fully formed objects) account naturally for the
formation of BD disks, avoid the problem of high ejection speeds implied in the
standard ejection models of point-sized objects, and are also consistent with the
observation of isolated low-mass clumps. In the ejection scenario, proto-BDs of
larger masses have a higher likelihood for survival, thus providing a possible
explanation for the IMF turnover at the lowmass end. Formation of wide-orbit BD
companions to stars can also be explained in the disk fragmentation scenario. However, the likelihood of survival of the fragments is low, particularly
at small orbital distances, which naturally accounts for the existence of the so-called BD desert.

Organisation(s)

Department of Astrophysics

External organisation(s)

University of Western Ontario

Journal

Memorie Societa Astronomica Italiana

Volume

84

Pages

866-874

No. of pages

8

ISSN

0037-8720

Publication date

2013

Peer reviewed

Yes

Austrian Fields of Science 2012

103004 Astrophysics

Portal url

https://ucrisportal.univie.ac.at/en/publications/ecb22080-2373-4269-be35-6187f504e82d