G2 and Sgr A*: A Cosmic Fizzle At The Galactic Center

Abstract

We carry out a series of simulations of G2-type clouds interacting with the black hole at the galactic center, to determine why no large changes in the luminosity of Sgr A* were seen, and to determine the nature of G2. We measure the accretion rate from the gas cloud onto Sgr A* for a range of simulation parameters, such as cloud structure, background structure, background density, grid resolution, and accretion radius. For a broad range of parameters, the amount of cloud material accreted is small relative to the amount of background material accreted. The total accretion rate is not significantly effected for at least 30 years after periapsis. We find that reproducing observations of G2 likely requires two components for the object: an extended, cold gas cloud responsible for the Br-gamma emission, and a compact core or dusty stellar object dominating the bolometric luminosity. In simulations, the bolometric and X-ray luminosity have a peak lasting from about 1 year before to 1 year after periapsis, a feature not detected in observations. Our simulated Br-gamma emission is largely consistent with observations leading up to periapsis, with a slight increase in luminosity and a large increase in the FWHM of the line velocity. All emission from a gaseous component of G2 should fade rapidly after periapsis and be undetectable after 1 year, due to shock heating and expansion of the cloud. Any remaining emission should be from the compact component of G2.