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Simulations of orbiting and in-falling matter

SgrA* exhibits flaring activity across all observed bands. The typical duration of these outbursts is around one hour. The size of the emitting region can be estimated at first order considering the propagation distance of a light signal over that time. These light-travel arguments indicate that the source must be confined in a small region of 10-20 times the size of the black hole itself (Schwarzschild radius). One of the possible physical mechanisms is the magnification produced by the motion of bright clumps around the supermassive black hole. Gravito-magnetohydrodynamic simulations show that such clumps or hot-spots can be formed due to inhomogeneities and/or magnetic reconnection events in the mid-plane of the accretion flow. The size of one of those hot spots is comparable to the star Arcturus. The characteristic ligh curve of orbiting hot spots, shaped by the black-hole lensing and the Doppler boosting, can be observed in the brightest X-ray flares. The comparison between real data and simulations of orbiting/in-falling matter allows us to better understand the accretion process in the nearest supermassive black hole, SgrA*.

Example of a simulated SgrA* light curve. The background image is an artist impression of the inner region of an accretion flow where a hot clump orbits a supermassive black hole (BH). Top-right inset is a view from above of an orbiting hot spot, at two different radii, showing the positions where its emission would be largely enhanced due to lensing (L) and Doppler busting (D), producing the light curve shown at the bottom.

Credits: Eckart group, Ph1-UniKoeln.

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