Horizon-Scale Imaging of Supermassive Black Holes

In April 2019 the Event Horizon Telescope (EHT) collaboration, using sub-mm very-long-baseline interferometry (VLBI), presented the first "image" of the supermassive black hole M87, capturing an image of the hot, luminous matter swirling around it.

By coupling general-relativistic radiation transport (GRRT) calculations using my own GRRT code BHOSS (Younsi et al. 2019, in prep.) with the results of general-relativistic magnetohydrodynamical (GRMHD) simulations from BHAC (Porth et al., 2017), we can construct "infinite resolution" images of what we have now seen. If you are interested in using BHOSS, send me an email - it will soon also be made available on GitHub.

The panel below shows a sequence of five images of the black hole shadow (dark ring) surrounded by a bright accretion flow, as predicted for the black hole in our Galactic Centre, Sagittarius A* (Sgr A*), which the EHT soon anticipates to also resolve. All images are as seen at the EHT observing frequency of 230 GHz (1.3 mm wavelength) 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.