PKS 1830−211

PKS 1830−211 is a gravitationally-lensed blazar in the southern constellation of Sagittarius, one of the most powerful such objects known. This flat-spectrum radio quasar (FSRQ) has a high redshift of 2.507 and is among the brightest extraterrestrial radio sources. It was first detected in 1969 during a radio survey by the Parkes Observatory in Australia. In 1984, interplanetary scintillation was observed, indicating structure on angular scales of less than an arc second. Radio observations in 1988 revealed an unusual double structure separated by about 1 arc second, suggestive of gravitational lensing by a foreground galaxy. An unusually bright Einstein ring was detected in 1991 via interferometric radio telescope observation. The lens galaxy was identified in 2002 by the Hubble Space Telescope as a normal spiral galaxy at a redshift of 0.886, inclined at 25° to the plane of the sky and with a mass comparable to the Milky Way. A third point-like lensed image of the quasar was detected in 2020. PKS 1830−211 is a source for gamma-ray emission that undergoes significant flaring and, as of 2014, is the extragalactic object with the largest number of detected molecular species.