TON 618is a very distant and extremely luminous quasar—technically, a hyper luminous, broad-absorption line, radio-loud quasar—located near the North Galactic Pole in the constellation Canes Venatici. It contains one of the most massive known black holes, with a mass of 66 billion.
Because quasars were not recognized until 1963,[3] the nature of this object was unknown when it was first noted in a 1957 survey of faint blue stars (mainly white dwarfs) that lie away from the plane of the Milky Way. On photographic plates taken with the 0.7m Schmidt telescope at the Tonantzintla Observatory in Mexico, it appeared "decidedly violet" and was listed as number 618 in the Tonantzintla catalogue.[4]
In 1970, a radio survey at Bologna discovered radio emission from TON 618, indicating that it was a quasar.[5] Marie-Helene Ulrich then obtained optical spectra of TON 618 at the McDonald Observatory which showed emission lines typical of a quasar. From the redshift of the lines Ulrich deduced that TON 618 was very distant, and hence was one of the most luminous quasars known to man.[6]
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