Flaring Activity of the Black Hole at the Center of the Galaxy

Farhad Yusef-Zadeh (Northwestern University)

April 11, 2025

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Abstract: It is clear that an under-luminous supermassive black hole (Sgr A*) with a mass of 4.2 million solar mass lies at the center of the Galaxy. Precise measurements taken at radio and infrared wavelengths over the last two decades have led to this conclusion. The recent studies indicate deviations from Keplerian motion of a star orbiting the black hole, the precession of an orbiting star, and an image of the shadow of the black hole. These measurements are consistent with the predictions of the Einstein’s general theory of relativity. I will present highlights of recent James Webb Space Telescope (JWST) observations to study the flaring activity of the black hole. The variability of the black hole probes the process of the accretion flow at a distance of few Schwarszchild radius before running across the event horizon. These observations indicate that the flux of Sgr A* is fluctuating constantly punctuated with multiple synchrotron flares per day. I will argue that two distinct populations of particles produce bright and faint synchrotron variable emission. As for the origin of the infrared flares, a number of recent simulations suggest that flares are ejected plasmoids from the accretion disk due to the reconnection of the magnetic field lines. Time permitting, I will also discuss the relationship between radio/submm, X-ray and infrared variable emission.