The First Black Hole Shadow Image
The first ever image of a black hole shadow in the human history. The image is a supermassive black hole at the center of an elliptical galaxy M87 at the center of the Virgo cluster (EHT Collaboration et al. 2019, ApJL, 875, L1).
The image of the black hole shadow provided the accurate black hole mass estimation (6.5 billion times the mass of the Sun) from the size of the ring (42 micro-arcsec, or 0.000000012 degree) with considering the General Relativity, and the brighter in the lower side of the ring is highly due to the Doppler boosting of the light (gravitational blue shift on the lower half of the ring).