Astronomers Capture First Image of a Black Hole | ESO "ESO, ALMA, and APEX contribute to paradigm-shifting observations of the gargantuan black hole at the heart of the galaxy Messier 87"
Black Hole Image Makes History; NASA Telescopes Coordinate Observation | NASA
What we see is the glow of the hot material traveling near the black hole, with the BH itself obstructing part of it. The ring shape is from the BH strongly deflecting light around its event horizon. The dark area is more-or-less the BH's shadow.
The
Event Horizon Telescope is a collaboration of astronomers all over the world who combine the outputs of their radio telescopes to make those telescopes act like a single, Earth-sized telescope. This technique, VLBI, is not new, but what is new here is the attempt to image central black holes of galaxies. The telescopes' combined resolution is 20 microarcseconds, or 10^(-10) radians.
The picture is for
Messier 87, a giant elliptical galaxy some 53.5 ± 1.63 Mly (16.40 ± 0.50 Mpc) away. It is the brightest galaxy in the nearby Virgo Cluster of galaxies, and its mass inside 100 kpc (300 kly) is about 10^13 solar masses, about 10 times that of our Galaxy.
From the recent observation of it, the central black hole's mass is (6.5 ± 0.2stat ± 0.7sys) billion solar masses, in rough agreement with previous estimates. Its black-hole radius is about 20 billion kilometers (20 terameters) or 130 AU's. This corresponds to an angular radius of 4*10^(-11) radians, making it borderline visible.
By comparison, the black hole in the center of our Galaxy is about 4 million solar masses, with a black-hole radius of 1.2*10^7 kilometers (12 gigameters), or 0.08 AU's. This gives an angular radius of 5*10^(-11) radians, also making it borderline visible.
The Andromeda Galaxy's black hole has something from 50 to 200 million solar masses, and choosing 100 million for definiteness gives a black-hole radius of 300 million km (300 Gm), or 2 AU. This gives an angular radius of 10^(-11) radians, a bit small.
