Einstein Cross (QSO J2240+0321)
![QSO J2240+0321](/pic/nsf/qso_j2240+0321_noao-q2237.jpg)
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.
![G 2237+0305](/thumb/15175dd3dbe41f09a0a7eb641e6782db_fig.webp)
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.
![Finder Chart Einstein Cross (QSO J2240+0321)](/pic/charts/qso_j2240+0321_chart.webp)
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