The Properties of Prestellar Discs in Isolated and Binary Prestellar Systems

We present high-resolution 3D smoothed particle hydrodynamics simulations of the formation and evolution of protostellar discs in a turbulent molecular cloud. Using a piecewise polytropic equation of state, we follow the evolution of an isolated and a binary protostellar system in the same environment. In both cases the discs are sufficiently massive to develop gravitational instabilities. The isolated system accretes gas with steadily increasing specific angular momentum until an m = 2 mode develops into material arms that fragment, forming clumps with initial masses of 5.5 Mjup and 7.4 Mjup, and growing to masses of 39 Mjup and 14 Mjup, respectively. The clumps have typical accretion rates of 10^(-5) Msol/yr. While the discs in the binary system are strongly self-gravitating, we find that they are stable against fragmentation due to disc truncation and mass profile steeping by tides, accretion of high specific angular momentum gas by the secondary, and angular momentum being redirected into the binary's orbit.