Relaxation of protostellar accretion shocks using the smoothed particle hydrodynamics

TL;DR

This study uses smoothed particle hydrodynamics to analyze how quickly post-shock gas in protostellar accretion processes cools and forms dense disks, which are crucial for planet formation.

Contribution

It introduces a simplified one-dimensional model to simulate shock relaxation and cooling in protostellar accretion, highlighting the formation of dense molecular disks.

Findings

Post-shock temperature rises rapidly with Mach number

Cooling leads to the formation of thin dense molecular disks

Conditions favorable for grain growth and planet formation are established

Abstract

It is believed that protostellar accretion disks to be formed from nearly ballistic infall of the molecular matters in rotating core collapse. Collisions of these infalling matters lead to formation of strong supersonic shocks, which if they cool rapidly, result in accumulation of that material in a thin structure in the equatorial plane. Here, we investigate the relaxation time of the protostellar accretion post-shock gas using the smoothed particle hydrodynamics (SPH). For this purpose, a one-dimensional head-on collision of two molecular sheets is considered, and the time evolution of the temperature and density of the post-shock region simulated. The results show that in strong supersonic shocks, the temperature of the post-shock gas quickly increases proportional to square of the Mach number, and then gradually decreases according to the cooling processes. Using a suitable cooling function shows that in appropriate time-scale, the center of the collision, which is at the equatorial plane of the core, is converted to a thin dense molecular disk, together with atomic and ionized gases around it. This structure for accretion disks may justify the suitable conditions for grain growth and formation of proto-planetary entities.