Recoating Yepun's mirror

Rotation curve (velocity vrs. distance from the centre) of the disk surrounding the black hole at the centre of Centaurus A . From the ISAAC spectrum displayed in ESO Press Photo eso0109, the `average' gas velocities along the slit direction can be derived. Position `0' on the horizontal axis indicates the exact position of the galaxy nucleus; at the distance of Centaurus A, 1 arcsec corresponds to 55.5 light-years (17 pc). The blue triangles and the red squares correspond to emission lines from singly ionized Iron atoms ([Fe II]) and Hydrogen (Paschen-Beta), respectively. The high velocities are the hallmark of a central black hole. The thick solid line represents the expected velocities, assuming the presence of a 200 million solar-mass black hole at the centre.