The Optical Spectral Signature of a Black Hole
On the left is the core of the galaxy M84. The spectral scan box in light blue on the left shows stars and gas within 26 light-years of the galaxy's center rapidly swirling around a ~3x108 Solar mass black hole. The figure on the right represents the velocity of the swirling matter, with a dramatic reversal when the scan passes through the massive object at the center.