Abell 2218

Abell 2218
250px Abell 2218. Credit: NASA/ESA
Observation data (Epoch J2000)
Constellation(s)	Draco
Right ascension	16h 35m 54s
Declination	+66° 13′ 00″
Number of galaxies	~10,000
Richness class	4
Bautz-Morgan classification	II
Redshift	0.17560
Distance (co-moving)	719 Mpc (2,345 Mly) h−1 0.705
X-ray flux	(7.50 ± 9.1%)×10−12 erg s−1 cm−2 (0.1—2.4 keV)
See also: Galaxy groups, Galaxy clusters, List of galaxy clusters

Abell 2218 is a cluster of galaxies about 2 billion light-years away in the constellation Draco.

Acting as a powerful lens, it magnifies and distorts all galaxies lying behind the cluster core into long arcs. The lensed galaxies are all stretched along the cluster's center and some of them are multiply imaged. Those multiple images usually appear as a pair of images with a third — generally fainter — counter image, as is the case for the very distant object. The lensed galaxies are particularly numerous, as we are looking in between two mass clumps, in a saddle region where the magnification is quite large.

Gravitational lensing

Abell 2218 was used as a gravitational lens to discover the most distant known object in the universe as of 2004. The object, a galaxy some 13 billion years old, is seen from Earth as it would have been just 750 million years after the Big Bang.

The color of the lensed galaxies is a function of their distances and types. The orange arc is an elliptical galaxy at moderate redshift (z=0.7). The blue arcs are star-forming galaxies at intermediate redshift (z=1-2.5). The encircled very red pair is the newly discovered star-forming galaxy at about redshift 7.

See also

• Abell 370
• Abell 1835 IR1916
• GRB 090423
• IOK-1
• UDFy-38135539
• X-ray astronomy

External links

• Release about Abell 2218 at ESA/Hubble
• Astronomy Picture of the Day - Abell 2218: A Galaxy Cluster Lens - 2010 June 20