On the diversity and statistical properties of protostellar discs

Abstract

We present results from the first population synthesis study of protostellar discs. We analyse the evolution and properties of a large sample of protostellar discs formed in a radiation hydrodynamical simulation of star cluster formation. Due to the chaotic nature of the star formation process, we find an enormous diversity of young protostellar discs, including misaligned discs, and discs whose orientations vary with time. Star-disc interactions truncate discs and produce multiple systems. Discs may be destroyed in dynamical encounters and/or through ram-pressure stripping, but reform by later gas accretion. We quantify the distributions of disc mass and radii for protostellar ages up to ≈ 10 5 yrs. For low-mass protostars, disc masses tend to increase with both age and protostellar mass. Disc radii range from of order ten to a few hundred au, grow in size on timescales ∼ < 10 4 yr, and are smaller around lower-mass protostars. The radial surface density profiles of isolated protostellar discs are flatter than the minimum mass solar nebula model, typically scaling as Σ ∝ r −1. Disc to protostar mass ratios rarely exceed two, with a typical range of M d /M * = 0.1−1 to ages ∼ < 10 4 yrs and decreasing thereafter. We quantify the relative orientation angles of circumstellar discs and the orbit of bound pairs of protostars, finding a preference for alignment that strengths with decreasing separation. We also investigate how the orientations of the outer parts of discs differ from the protostellar and inner disc spins for isolated protostars and pairs.

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

“…We made sure that the final star-disk angle ψ sd is well converged to the value without implementing the procedure, while the amplitude of the stellar spin is significantly suppressed. In addition, as shown by Bate (2018), the star-disk misalignment can be captured even without the sub-grid model in the calculation of the Table 1. The model names and parameters which characterize the initial molecular cloud core; α = E thermal / |E grav |, γ turb = E turb / |E grav |, β eff is the dimensionless angular momentum, R init and ρ init = 3M init /(4π R 3 init ) are the initial radius and density of the cloud cores, M is the mean Mach number, t ff = 3π/(32Gρ init ) is the free-fall time of the initial cloud cores, ψ sd (t = 10 2 yr) and ψ sd (t = 10 5 yr) are the star-disk angles measured at t = 10 2 yr and t = 10 5 yr from the protostar formation epoch.…”

Massive discs around low-mass stars

“…We computed the time evolution of discs around 0.1 and 1.0 M stars, with initial disc-to-star mass ratios of ∼ 1 and an outer radius of 100 AU. This initial disc mass is high, but such values do appear in the simulations of star formation that naturally produce discs (Bate 2018). The evolution of the disc-to-star mass ratio and self-gravitationally driven effective α viscosity is given for each model in Figure 1.…”

Formation of planetary populations − II. Effects of initial disc size and radial dust drift

“…Quantifying disk properties has also been approached numerically in Bate (2018), who used radiative hydrodynamic calculations to compute distributions of disk masses and radii resulting from protostellar collapse. This work shows that initial disk radii significantly larger than ∼ 70 AU are uncommon.…”