Nandra said this emission is typical of a black hole observation. Buried in the typical emission spectrum, however, was a rare glimpse at a red-shifted absorption feature also from iron atoms. You often see evidence of matter flying out of a black hole, but never falling in. For example, with ultraviolet telescopes, one also detects absorption lines. But this is always from matter moving toward us and not into a black hole.
Scientists have many tools to understand the properties of a distant light source.
Among these tools are the emission spectrum and the Doppler effect. The emission spectrum is a breakdown of light into its component colors, much like a prism separates white light into a rainbow. This provides information about the type of gas emitting the light, as well as its velocity, temperature and pressure. The emission from NGC 3516 comes from a blur of gas molecules or atoms moving in many directions. The Doppler effect is the same phenomenon that distorts the sound of the horn on a speeding car as it approaches and passes you a highway.