The Outcome of Collisions between Gaseous Clumps formed by Disk Instability

TL;DR

This study uses advanced simulations to analyze collisions between gaseous clumps in disk instability, revealing that perfect mergers are rare and outcomes often involve erosion, disruption, or hit-and-run, impacting planet formation models.

Contribution

It provides detailed simulation-based insights into collision outcomes of gaseous clumps, challenging the common perfect merger assumption in population synthesis models.

Findings

Most collisions lead to erosion, disruption, or hit-and-run outcomes.

Collisions can sometimes trigger dynamical collapse of clumps.

The perfect merger assumption is rarely valid in these scenarios.

Abstract

The disk instability model is a promising pathway for giant planet formation in various conditions. At the moment, population synthesis models are used to investigate the outcomes of this theory, where a key ingredient of the disk population evolution are collisions of self-gravitating clumps formed by the disk instabilities. In this study, we explore the wide range of dynamics between the colliding clumps by performing state-of-the-art Smoothed Particle Hydrodynamics simulations with a hydrogen-helium mixture equation of state and investigate the parameter space of collisions between clumps of different ages, masses (1--10 Jupiter mass), various impact conditions (head-on to oblique collisions) and a range of relative velocities. We find that the perfect merger assumption used in population synthesis models is rarely satisfied and that the outcomes of most of the collisions lead to erosion, disruption or a hit-and-run. We also show that in some cases collisions can initiate the dynamical collapse of the clump. We conclude that population synthesis models should abandon the simplifying assumption of perfect merging. Relaxing this assumption will significantly affect the inferred population of planets resulting from the disk instability model.