# A 3D Hydrodynamics Study of Gravitational Instabilities in a Young Circumbinary Disc

## TL;DR

This study uses 3D hydrodynamics simulations to analyze gravitational instabilities in a young circumbinary disc, revealing how a brown dwarf companion influences disc dynamics and evolution.

## Contribution

It provides the first detailed comparison of GIs in circumbinary versus single-star protoplanetary discs using radiative 3D hydrodynamics simulations.

## Key findings

- Binarity causes more violent initial GIs due to a strong one-armed density wave.
- Both discs reach similar quasi-steady states after 2,500 years.
- Binarity affects gravitational torques, temperature profiles, and mass transport, influencing planet formation.

## Abstract

We present a 3D hydrodynamics study of gravitational instabilities (GIs) in a 0.14 M$_{\odot}$ circumbinary protoplanetary disc orbiting a 1 M$_{\odot}$ star and a 0.02 M$_{\odot}$ brown dwarf companion. We examine the thermodynamical state of the disc and determine the strengths of GI-induced density waves, nonaxisymmetric density structures, mass inflow and outflow, and gravitational torques. Results are compared with a parallel simulation of a protoplanetary disc without the brown dwarf binary companion. Simulations are performed using CHYMERA, a radiative 3D hydrodynamics code. The onset of GIs in the circumbinary disc is much more violent due to the stimulation of a strong one-armed density wave by the brown dwarf. Despite this early difference, detailed analyses show that both discs relax to a very similar quasi-steady phase by 2,500 years after the beginning of the simulations. Similarities include the thermodynamics of the quasi-steady phase, the final surface density distribution, radial mass influx, and nonaxisymmetric power and torques for spiral arm multiplicities of two or more. Effects of binarity in the disc are evident in gravitational torque profiles, temperature profiles in the inner discs, and radial mass transport. After 3,800 years, the semimajor axis of the binary decreases by about one percentage and the eccentricity roughly doubles. The mass transport in the outer circumbinary disc associated with the one-armed wave may influence planet formation.