Star–disc alignment in the protoplanetary discs: SPH simulation of the collapse of turbulent molecular cloud cores

Abstract

ABSTRACT We perform a series of three-dimensional smoothed particle hydrodynamics (SPH) simulations to study the evolution of the angle between the protostellar spin and the protoplanetary disc rotation axes (the star–disc angle ψsd) in turbulent molecular cloud cores. While ψsd at the protostar formation epoch exhibits broad distribution up to ∼130°, ψsd decreases (≲ 20°) in a time-scale of ∼104 yr. This time-scale of the star–disc alignment, talignment, corresponds basically to the mass doubling time of the central protostar, in which the protostar forgets its initial spin direction due to the mass accretion from the disc. Values of ψsd both at t = 102 yr and t = 105 yr after the protostar formation are independent of the ratios of thermal and turbulent energies to gravitational energy of the initial cloud cores: α = Ethermal/|Egravity| and γturb = Eturbulence/|Egravity|. We also find that a warped disc is possibly formed by the turbulent accretion flow from the circumstellar envelope.