Anna Ciurlo: Gas Dynamics in the Galactic Center
UCLA Galactic Center Group
The center of our Galaxy, because of its proximity, is a unique and exemplary laboratory to study the energetic phenomena taking place in the heart of galaxies. The galactic supermassive black hole is not very bright but it was perhaps more active a few hundred years ago.
Recently, observations in the radio highlighted the presence of an accretion disk at ~0.01 pc. However, I established that there is no infrared counterpart to such accretion disk, requiring an amplification by maser to justify the radio emission.
The largest reservoir of material that could trigger a more intense phase is a molecular gas torus at about 1 pc. However, Smaller-scale processes can accrete material onto the black hole and potentially trigger short peaks in the activity.
In the central few tenth of a parsec, I highlighted several compact sources in orbit around the central supermassive black hole. These objects appear to have the emission properties of gas clouds but they also exhibit the dynamical behavior of stars. Two of such objects were previously known and largely debated (especially the tidally-interacting G2) but the discovery of four additional sources demonstrates the existence of a population that requires a common formation mechanism. The explanation best fitting the dynamics of the region is that the G-objects are residuals of binary star systems merged under the influence of the supermassive black hole. However the debate on the origin of these sources is still open. Another source orbits the black hole on a similar scale but shows a very different morphology, maybe due to the interaction with a jet. Some of these objects can transport material to the black hole and cause an increase in its activity. We did observe a peak in activity last summer that could be connected with the close passage of G2.
Processes at different scales highlight the complexity and interconnection of the mechanisms in the Galactic Center and the study of the interstellar medium at both small and large scale represent an important piece in understanding the environment of a supermassive black hole.