Speaker: Nicolas Aimar (CENTRA, Instituto Superior Técnico)
Title: Why Sagittarius A* flares are so difficult to model?
Abstract: The center of our galaxy hosts a supermassive black hole SMBH of 4.3 millions solar masses called Sagittarius A* (Sgr A*). Its mass and proximity are making the galactic center the ideal laboratory to study General Relativity (GR) from parsec scale to few gravitational radii. Orbits of close stars (S-Stars) allowed recently to detect the gravitational Doppler effect and Swcharzschild precession around a SMBH. To test GR in the strongest regime, we need to go even closer to the SMBH, by studying the bright and short outbursts of radiation from Sgr A* called flares. Indeed, in 2018, the GRAVITY Collaboration reported the detection of orbital motion of flares around the black hole. These flares have been observed since 2003 from radio to X-ray with puzzling properties. Numerous models have been developed to explain Sgr A* without reaching a clear consensus. In the last few years, magnetic reconnection appears as the most promising scenario to explain the flares of Sgr A*.
However, properly model Sgr A* flares is a very difficult task as it imply a lot of different physical field among them, some are poorly constrained. In this talk, I will present all the challenges that arise from modelling Sgr A* flares and how can they be used to study GR.