Dr. P. Chris Fragile
-Disruption of Galactic Center Cloud G2-
Recently, my research group worked with collaborators from Lawrence Livermore National Laboratory on a series of 3D simulations to study the fate of a newly discovered gas cloud moving through the Galactic Center. The cloud, known as G2, is on an orbit that is expected to take it within 40 billion kilometers (270 AU) of Sgr A* in June of next year, near enough to undergo significant disruption by the black hole's gravitational forces. This will provide an unprecedented opportunity to study the interaction of a gas cloud with the gravitational potential near Sgr A* and the background environment of the Galactic Center.
The simulations test several possible scenarios for the specific characteristics of the cloud and the background gas, including the equation of state, density and pressure profiles of the background, and start times for the evolution. This way, they help predict a range of different ways G2's destruction will unfold through the year 2020, as well as the effect it may have on Sgr A*'s activity. This is important since, for its size, Sgr A* is the most underluminous black hole known, as it has long been underfed. The accretion of gas from G2 may, therefore, have significant effect its luminosity.
Our results show that the cloud will begin to experience significant disruption starting in 2013. At the start, the cloud is modeled as a simple gas sphere near the point in its orbit where it was first discovered in 1995, or at its orbital apocenter in 1944. As it approaches Sgr A*, tidal stretching increasingly distorts the cloud, stretching it along its trajectory. By the end of 2012, it will be nearly five times longer than it is wide. Along with tidal stretching, the cloud experiences ram pressure forces as it tries to plow through background gas, and hydrodynamic interactions with this material cause further disruptions. Collectively, these effects gradually strip material from the cloud and feed it into Sgr A*, beginning in 2013. The measured accretion rate of cloud material in the simulations would represent a boost to Sgr A*'s current accretion rate of only 1-5%. However, a rough estimate of the luminosity from the destruction of the cloud itself shows that it may be bright enough to be observable.
3D volume visualizations of one of the simulated clouds at five points in its evolution from 2010 to 2020. The color corresponds to the density of cloud material, and the gray sphere represents the point beyond which gas is considered accreted by the black hole.