Three-Dimensional Moving-Mesh Simulations of Galactic Center Cloud G2

TL;DR

This study uses 3D moving-mesh simulations to predict the evolution of the G2 gas cloud near the galactic center, assessing its impact on Sgr A*'s activity and potential observability.

Contribution

First detailed 3D moving-mesh simulations of G2's evolution considering various parameters and their implications for accretion and activity at Sgr A*.

Findings

Estimated accretion rate of 5-19 x 10^{-8} solar masses per year from 2013 to 2020.

Accretion variability less than a factor of three on <1 month timescales.

Minimal increase (<5%) in current accretion rate at Sgr A* due to G2 breakup.

Abstract

Using three-dimensional, moving-mesh simulations, we investigate the future evolution of the recently discovered gas cloud G2 traveling through the galactic center. We consider the case of a spherical cloud initially in pressure equilibrium with the background. Our suite of simulations explores the following parameters: the equation of state, radial profiles of the background gas, and start times for the evolution. Our primary focus is on how the fate of this cloud will affect the future activity of Sgr A*. From our simulations we expect an average feeding rate in the range of $5-19 \times 10^{-8}$ solar masses per year beginning in 2013 and lasting for at least 7 years (our simulations stop in year 2020). The accretion varies by less than a factor of three on timescales <1 month, and shows no more than a factor of 10 difference between the maximum and minimum. These rates are comparable to the current estimated accretion rate in the immediate vicinity of Sgr A*, although they represent only a small (<5%) increase over the current expected feeding rate at the effective inner boundary of our simulations. Therefore, the break up of cloud G2 may have only a minimal effect on the brightness and variability of Sgr A* over the next decade. This is because current models of the galactic center predict that most of the gas will be caught up in outflows. However, if the accreted G2 material can remain cold, it may not mix well with the hot, diffuse background gas, and instead accrete efficiently onto Sgr A*. Further observations of G2 will give us an unprecedented opportunity to test this idea. The break up of the cloud itself may also be observable. By tracking the amount of cloud energy that is dissipated during our simulations, we are able to get a rough estimate of the luminosity associated with its tidal disruption; we find values of a few $10^{36}$ erg/s.