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

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.

• The paper uses three-dimensional moving-mesh simulations to study the gas cloud G2's interaction and evolution near the galactic center black hole Sgr A*.
• Simulations estimate Sgr A* accretion rates from G2 at $5-19 imes 10^{-8} M_\odot~\mathrm{yr}^{-1}$ and predict minimal impact on its brightness.
• Three-dimensional simulations reveal complex tidal and ram pressure disruption processes for G2, highlighting the importance of 3D modeling.

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

The paper deals with the comprehensive study of the evolution of the gas cloud G2 as it travels through the galactic center near Sgr A*, utilizing three-dimensional moving-mesh simulations to capture the complex interplay of dynamics involved. The primary focus is on understanding the cloud's interaction with the environment near the supermassive black hole at the Milky Way's center and the implications this has for the future activity of Sgr A*.

The authors simulate a spherical cloud starting in pressure equilibrium with its surroundings. Critical parameters in the simulations include the cloud's equation of state, the radial profiles of the background gas, and varying start times for the cloud's evolution. These simulations provide insights into potential accretion rates of material onto Sgr A*, estimated to be between $5-19 \times 10^{-8} M_\odot~\mathrm{yr}^{-1}$, starting in 2013 and projected to last for at least seven years based on the simulations' timeframe till 2020. Interestingly, accretion variability does not exceed a factor of three monthly and a factor of ten from peak to minimum within each model, indicating relatively stable feeding rates.

A significant finding is that the expected increase in Sgr A*'s feeding rate is minimal ($\lesssim 5$\% at the inner boundary of simulations, $r = 750 R_S \approx 10^{15}$~cm), thus suggesting negligible impact on its brightness and variability over the next decade. However, the possibility that cold G2 material might accrete more efficiently, remaining distinct from the hot, diffuse background, presents an area for further observation and exploration.

The simulations showcase various physical processes affecting G2, such as tidal stretching, hydrodynamic instabilities, and cloud breakup due to the combination of tidal and ram pressure forces. A crucial insight derived is the importance of three-dimensional modeling, as the simulations reveal more complex and varied cloud disruption phenomena than two-dimensional counterparts.

Theoretical implications are significant as they provide a real-case laboratory for studying extreme accretion phenomena. Observationally, G2's breakup presents a unique opportunity to test models of Sgr A* accretion physics. Future implications of this work largely hinge on improving simulations by incorporating additional factors such as magnetic fields or alternative scenarios of the cloud's origin, which could refine predictions of its impact on Sgr A*.

This research exemplifies the utility of detailed simulations in understanding astrophysical phenomena and highlights the potential of such methodologies to refine our comprehension of galactic nucleus dynamics and accretion physics. Speculation about future developments in AI might involve more advanced simulations that include machine learning techniques to better predict fluid dynamics in these scenarios.