Horizon-Scale Imaging of Sgr A*

Soon astronomers, using the Event Horizon Telescope (EHT) and sub-mm very-long-baseline interferometry (VLBI) anticipate obtaining the first image of an astrophysical black hole, specifically the black hole in our Galactic Centre, Sagittarius A* (Sgr A*). By coupling general-relativistic radiation transport (GRRT) calculations using my own GRRT code BHOSS with the results of general-relativistic magnetohydrodynamical (GRMHD) simulations from BHAC, we can construct "infinite resolution" images of what we soon expect to see.

The panel below shows a sequence of five images of the black hole shadow (dark ring) surrounded by a bright accretion flow. All images are as seen at the EHT observing frequency of 230 GHz and the colour scale is black through purple to white (brightest). The sequence of images is for a black hole of high spin parameter (a=0.9375) and at viewing inclination angles of 15°, 45°, 60° and 90° respectively.

The left side of the image is brightened due to Doppler beaming as the black hole is spinning towards the observer (in an anticlockwise sense). Similarly, the receding side is dimmed. As the viewing inclination angle increases the black hole shadow shifts to the right and deforms from a circular to a right-asymmetric profile (e.g. 85° and 90°). It is this asymmetric distribution of brightness in the image along with a inner dim (shadow) region which we hope to observe.