Library of quasars reveals unknown patterns

Ars Technica : Quasars are black holes that pull in massive amounts of matter, shine brightly across the electromagnetic spectrum, and emit jets of extremely high-energy particles. They have been hard to categorize, however, because of their wide range of appearances and characteristics. Now, Yue Shen and Luis C. Ho of Peking University have compiled a database of more than 20 000 quasars found by the Sloan Digital Sky Survey. They recorded the quasars’ spectra, the orientation of their accretion material, and a characteristic called the Eddington ratio , which compares a quasar’s luminosity with its theoretical maximum and thus is a measure of the accretion efficiency. By comparing the disk orientation with accretion efficiency and spectral line strength, they created a graph that fits all of the quasars into a well-defined, orderly plot. Determining the cause of the distinctive pattern could provide significant insight into the properties of quasars. Separately, the study found that the highest-mass quasars (the ones with the lowest Eddington ratios) are clustered together, which hints at some connection between quasars and the large-scale structure of the universe.