Typical QSO

Typical QSO spectrum

A typical SDSS spectrum of a quasi-stellar object (QSO). The lines that lie above average are the emission lines, used to determine the redshift of the QSO. (In this case, z = 2.495.) The narrow features that dip below the average, called absorption lines, represent absorption in intergalactic gas clouds between the Earth and the object. The labels at the top denote the element and the ionization stage to which the absorption lines belong.
Image credit: Don York, SDSS Collaboration

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