Einstein Cross (G2237+030)
The Einstein Cross (G2237+030) is the most spectacular of the well-attested instances of gravitational lenses that involve a quasar and foreground galaxy. The Einstein Cross consists of four symmetrically placed images of the same quasar, which lies 8 billion light-years away and almost directly behind the nucleus of a galaxy that is only 500 million light-years away. The alignment is so close that if the lens effect could be removed, the quasar would appear within 0.05" of the galaxy's nucleus. The system was discovered in the course of a redshift survey by the Smithsonian Center for Astrophysics by John Huchra (1948–), and is sometimes referred as the Huchra Lens. Einstein crosses form when source and lens are in alignment with the observer but the lensing mass is unevenly distributed. When there is alignment plus even distribution of the lensing mass the result is an Einstein ring.