Lensing and shadow of a black hole surrounded by a backreacting accretion disk
Presenting author: Nelson Eiró
We consider a static, axially symmetric spacetime describing the superposition of a Schwarzschild black hole (BH) with a thin, backreacting, accretion disk which is located at the equatorial plane. The phenomenology of the composed system depends on two parameters: the fraction of the total mass in the disk, m, and the location of the inner edge of the disk, a. We study the null geodesic flow by performing backwards ray-tracing under two scenarios. In the first (second) scenario the composed system is illuminated by the disk (a far-away celestial sphere). Both cases show that, as m grows, the shadow becomes more prolate. Additionally, the first scenario makes clear that as m grows, for fixed a, the geometrically thin disk appears optically enlarged, i.e. thicker, when observed from the equatorial plane. This is to due to light rays that are bent towards disk, when backwards ray traced. In the second scenario, these light rays can cross the disk (which is assumed to be transparent) and may oscillate up to a few times before reaching the far away celestial sphere. Consequently, an almost equatorial observer sees different patches of the sky near the equatorial plane.
Oral presentation: yes. Poster: no.