The formation of brown dwarfs and low-mass stars by disc fragmentation

Abstract

We suggest that a high proportion of brown dwarfs are formed by gravitational fragmentation of massive extended discs around Sun‐like stars. We argue that such discs should arise frequently, but should be observed infrequently, precisely because they fragment rapidly. By performing an ensemble of radiation‐hydrodynamic simulations, we show that such discs typically fragment within a few thousand years to produce mainly brown dwarfs (including planetary‐mass brown dwarfs) and low‐mass hydrogen‐burning stars. Subsequently most of the brown dwarfs are ejected by mutual interactions. We analyse the properties of these objects that form by disc fragmentation, and compare them with observations.