Spectrum of the quasar APM 08279+5255, showing iron-cloud traces
The left picture shows a photo of the quasar, taken by XMM-Newton. The dip in the spectrum of the quasar APM 08279+5255 is caused by the element iron. In a same way that our bones appear dark in X-ray photographs because they are opaque to X-rays, the outflowing iron clouds of APM 08279+5255 are opaque for X-rays that are created at the quasar's centre. At the 'absorption energy' characteristic for iron (marked by the red arrow), some part of the X-ray light is missing.