Einstein Cross

Common card · No. 380607

The Einstein Cross (Q2237+0305 or QSO 2237+0305) is a gravitationally lensed quasar that sits directly behind the centre of the galaxy ZW 2237+030, called Huchra's Lens. Four images of the same distant quasar (plus one in the centre, too dim to see) appear in the middle of the foreground galaxy due to strong gravitational lensing. This system was discovered by John Huchra and coworkers in 1985, although at the time they only detected that there was a quasar behind a galaxy based on differing redshifts and did not resolve the four separate images of the quasar. While gravitationally lensed light sources are often shaped into an Einstein ring, due to the elongated shape of the lensing galaxy and the quasar being off-centre, the images form a peculiar cross-shape instead. Other "Einstein crosses" have been discovered.

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