# Probing the Gas Density in our Galactic Center: Moving Mesh Simulations of G2

## TL;DR

This paper uses high-resolution moving mesh simulations to model the tidal disruption and emission of the G2 gas cloud in the Galactic Center, explaining observed luminosity and shape changes during pericenter passage.

## Contribution

It introduces detailed moving mesh simulations that reproduce G2's observed emission and morphology, providing new insights into its density, shape, and survival during pericenter.

## Key findings

- G2 is a tidally disrupted gas cloud with a density below 500 cm^{-3}.
- The cloud's elongation and luminosity match observations when modeled with appropriate densities.
- Simulations show the cloud survives pericenter passage with a shape consistent with observations.

## Abstract

The G2 object has recently passed its pericenter passage in our Galactic Center. While the $Br_\gamma$ emission shows clear signs of tidal interaction, the change in the observed luminosity is only of about a factor of 2, in contention with all previous predictions. We present high resolution simulations performed with the moving mesh code, RICH, together with simple analytical arguments that reproduce the observed $Br_\gamma$ emission. In our model, G2 is a gas cloud that undergoes tidal disruption in a dilute ambient medium. We find that during pericenter passage, the efficient cooling of the cloud results in a vertical collapse, compressing the cloud by a factor of $\sim5000$. By properly taking into account the ionization state of the gas, we find that the cloud is UV starved and are able to reproduce the observed $Br_\gamma$ luminosity. For densities larger than $\approx500\;\mathrm{cm}^{-3}$ at pericenter, the cloud fragments, due to cooling instabilities and the emitted radiation is inconsistent with observations. For lower densities, the cloud survives the pericenter passage intact and its emitted radiation matches the observed lightcurve. From the duration of $Br_\gamma$ emission which contains both redshifted and blueshifted components, we show that the cloud is not spherical but rather elongated with a size ratio of 4 at year 2001. The simulated cloud's elongation grows as it travels towards pericenter and is consistent with observations, due to viewing angles. The simulation is also consistent with having a spherical shape at apocenter.