Shuo Zhang, PhD, MIT

Supermassive black holes (SMBHs) may spend the majority of their lives accreting at low rates through radiatively inefficient, advection-dominated accretion flow. Therefore, low-luminosity SMBHs could greatly outnumber their more active cousins, active galactic nuclei, thus are essential for our understanding of SMBH activity cycles and their relationship to galaxy evolution. In particular, SMBHs harbored in local galaxies are found to be remarkably under-luminous. The best studied under-luminous SMBH is the closest such object to Earth, Sgr A*, located in the nucleus of our Milky Way galaxy. In this talk, I will introduce how we have been probing outburst history of Sgr A* and other SMBHs in nearby galaxies, to understand their activity cycle and accretion physics. We monitor Sgr A*'s nowadays X-ray activities and study its unique recurrent flaring activities occurring on daily basis. Using the X-ray emission from the 100 parsec molecular gas ring structure, we can infer Sgr A*'s activity history in the past a few hundred years. A larger molecular gas ring up to 1000 parsecs from the Galactic center helps to constrain Sgr A* activity up to a few thousand years ago. Lastly, a unique type of sources in the Galactic center, the non-thermal magnetic filaments, may carry footprint of a major particle outflow from Sgr A*, and indicate the SMBH as a powerful PeVatron.