Einstein Cross (QSO J2240+0321)
History
The spiral galaxy Z 378-15 (Z 2237.9+0305, CGCG 378-15, PGC 69457, LEDA 69457) first appeared in «Catalogue of galaxies and of clusters of galaxies» by Fritz Zwickys et al. which was published in 8 volumes from 1961 to 1968. [688]
In 1984 John Huchra et al. have discovered a gravitational lens which consists of a quasar nearly centered on the spiral galaxy. At 2" resolution, only a single optical image of the quasar was visible. [689] In 1986 at least two images of the lensed quasar could be identified. 1988 all three quasar images could be photographed using the 3.5m Canada-France-Hawaii telescope on Mauna Kea, Hawaii. [690]
The quasar is known referrad as QSO J2240+0321 (its J2000.0 position), QSO B2237+0305 or Q2237+0305 (its B1950.0 position), G 2237+0305 (G for gravitational lens), «Huchra's Lens» after its discoverer or «Einstein Cross» because it is an excellent example for gravitational lensing, postulated by Albert Einstein.
Physical Properties
QSO J2240+0321 is a gravitationally lensed quasar which lies behind the nucleus of the spiral galaxy Z 378-15. The mass of the much closer galaxy (z = 0.0386, approximately 400 million light years) is bending the light, causing a lens-like effect resulting in 4 distinct images of the same more distant quasar at z = 1.695 (distance approximately 8 billion light-years). The four images have an angular separation of 1.6 arcseconds and undergo color and brightness variations with a time scale of only a day or so. [687]
Finder Chart
The galaxy Z 378-15 (PGC 69457) with the Quasar QSO J2240+0321 is located in the constellation Pegasus. It is in opposition to the sun on 31 August and can best be observed in the months of June to December.
Visual Observation
762 mm Aperture: The Einstein Cross, or the quasar QSO J2240+0321, appears slightly square-shaped, with its form constantly changing due to atmospheric turbulence. While individual points do flash, their location and identity cannot be determined. No single light points are clearly identifiable; instead, multiple light sources are spread out over an area. The host galaxy PGC 69457 appears faintly extended at medium magnification. — 30" f/3.3 SlipStream Dobsonian, Hasliberg, 20. 11. 2011, SQM 21.27, Eduard von Bergen