Editing Active galactic nucleus (section)

=== Radiatively inefficient AGN ===
There exists a class of "radiatively inefficient" solutions to the equations that govern accretion. Several theories exist, but the most widely known of these is the [[Advection Dominated Accretion Flow]] (ADAF).<ref>{{Cite journal |last1=Narayan |first1=R. |last2=Yi |first2=I. |date=1994 |title=Advection-Dominated Accretion: A Self-Similar Solution |journal=Astrophys. J. |volume=428 |pages=L13 |arxiv=astro-ph/9403052 |bibcode=1994ApJ...428L..13N |doi=10.1086/187381 |s2cid=8998323}}</ref> In this type of accretion, which is important for accretion rates well below the [[Eddington limit]], the accreting matter does not form a thin disc and consequently does not efficiently radiate away the energy that it acquired as it moved close to the black hole. Radiatively inefficient accretion has been used to explain the lack of strong AGN-type radiation from massive black holes at the centres of elliptical galaxies in clusters, where otherwise we might expect high accretion rates and correspondingly high luminosities.<ref>{{Cite journal |last1=Fabian |first1=A. C. |last2=Rees |first2=M. J. |date=1995 |title=The accretion luminosity of a massive black hole in an elliptical galaxy |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=277 |issue=2 |pages=L55–L58 |arxiv=astro-ph/9509096 |bibcode=1995MNRAS.277L..55F |doi=10.1093/mnras/277.1.L55 |s2cid=18890265 |doi-access=free}}</ref> Radiatively inefficient AGN would be expected to lack many of the characteristic features of standard AGN with an accretion disc.