Editing Quasar (section)

== Quasar subtypes ==
The [[Taxonomy (general)|taxonomy]] of quasars includes various subtypes representing subsets of the quasar population having distinct properties.

* '''Radio-loud quasars''' are quasars with powerful [[Astrophysical jet|jets]] that are strong sources of radio-wavelength emission. These make up about 10% of the overall quasar population.<ref name="peterson1997">{{cite book |last1=Peterson |first1=Bradley |title=Active Galactic Nuclei |date=1997 |publisher=Cambridge University Press |isbn=0-521-47911-8}}</ref>
* '''Radio-quiet quasars''' are those quasars lacking powerful jets, with relatively weaker radio emission than the radio-loud population. The majority of quasars (about 90%) are radio-quiet.<ref name="peterson1997"/>
* '''Broad absorption-line (BAL) quasars''' are quasars whose spectra exhibit broad absorption lines that are blue-shifted relative to the quasar's rest frame, resulting from gas flowing outward from the active nucleus in the direction toward the observer. Broad absorption lines are found in about 10% of quasars, and BAL quasars are usually radio-quiet.<ref name="peterson1997"/> In the rest-frame ultraviolet spectra of BAL quasars, broad absorption lines can be detected from ionized carbon, magnesium, silicon, nitrogen, and other elements.
* '''Type 2 (or Type II) quasars''' are quasars in which the accretion disc and broad emission lines are highly obscured by dense gas and [[Cosmic dust|dust]]. They are higher-luminosity counterparts of Type 2 Seyfert galaxies.<ref>{{cite journal |last1=Zakamska |first1=Nadia |display-authors=etal|title=Candidate Type II Quasars from the Sloan Digital Sky Survey. I. Selection and Optical Properties of a Sample at 0.3 < ''Z'' < 0.83 |journal=The Astronomical Journal |year=2003 |volume=126 |issue=5 |page=2125 |doi=10.1086/378610 |bibcode=2003AJ....126.2125Z |arxiv=astro-ph/0309551 |s2cid=13477694 }}</ref> 
* '''Red quasars''' are quasars with optical colors that are redder than normal quasars, thought to be the result of moderate levels of dust [[Extinction (astronomy)|extinction]] within the quasar host galaxy. Infrared surveys have demonstrated that red quasars make up a substantial fraction of the total quasar population.<ref>{{cite journal |last1=Glikman |first1=Eilat |display-authors=et al |title=The FIRST-2MASS Red Quasar Survey |journal=The Astrophysical Journal |date=2007 |volume=667 |issue=2 |page=673 |doi=10.1086/521073 |bibcode=2007ApJ...667..673G |arxiv=0706.3222 |s2cid=16578760 }}</ref>
* '''[[OVV quasar|Optically violent variable]] (OVV) quasars''' are radio-loud quasars in which the jet is directed toward the observer. Relativistic beaming of the jet emission results in strong and rapid variability of the quasar brightness. OVV quasars are also considered to be a type of [[blazar]].
* '''Weak emission line quasars''' are quasars having unusually faint emission lines in the ultraviolet/visible spectrum.<ref>{{cite journal |last1=Diamond-Stanic |first1=Aleksandar |display-authors=etal|title=High-redshift SDSS Quasars with Weak Emission Lines |journal=The Astrophysical Journal |date=2009 |volume=699 |issue=1 |pages=782–799 |doi=10.1088/0004-637X/699/1/782 |bibcode=2009ApJ...699..782D |arxiv=0904.2181 |s2cid=6735531 }}</ref>