Neha Patil

Einstein Cross

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Constellation  Pegasus
Declination  +3° 21′ 31″
Type  LeQ
Right ascension  22 40 30.3
Redshift  1.695
Einstein Cross
Distance  8,000,000,000 ly (2,500,000,000 pc)

The Einstein Cross (Q2237+030 or QSO 2237+0305) is a gravitational lensed quasar that sits directly behind ZW 2237+030, Huchra's Lens. Four images of the same distant quasar (plus one in the centre, too dim to see) appear around a foreground galaxy due to strong gravitational lensing.

While gravitationally lensed light sources are often shaped into an Einstein ring, due to elongated shape of the lensing galaxy and the quasar being off-centre, the images form a peculiar cross-shape instead.

The quasar's redshift indicates that it is located about 8 billion light years from Earth, while the lensing galaxy is at a distance of 400 million light years. The apparent dimensions of the entire foreground galaxy are 0.87 × 0.34 arcminutes, while the apparent dimension of the cross in its centre accounts for only 1.6x1.6 arcseconds.

The Einstein Cross can be found in Pegasus at 22h 40m 30.3s, +3° 21′ 31″.

Amateur astronomers are able to see some of the cross using telescopes but it requires extremely dark skies and telescope mirrors with diameters of 18 inches (46 cm) or greater.

The individual images are labelled A through D (i.e. QSO 2237+0305 A), the lensing galaxy is sometimes referred to as QSO 2237+0305 G.

References

Einstein Cross Wikipedia


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