Abell 2029 is a large cluster

Galaxy cluster

A galaxy cluster is a compact cluster of galaxies. Basic difference between a galaxy group and a galaxy cluster is that there are many more galaxies in a cluster than in a group. Also, galaxies in a cluster are more compact and have higher velocity dispersion. One of the key features of cluster is...

 of galaxies

Galaxy

A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...

 a billion light years away in the constellation Virgo

Virgo (constellation)

Virgo is one of the constellations of the zodiac. Its name is Latin for virgin, and its symbol is . Lying between Leo to the west and Libra to the east, it is the second largest constellation in the sky...

. The central galaxy (IC 1101

IC 1101

IC 1101 is a supergiant lenticular galaxy at the center of the Abell 2029 galaxy cluster. It is 1.07 billion light years away in the constellation of Serpens and is classified as a cD class of galaxy.-Size:...

) is perhaps the largest known, with estimates ranging from 5.6 to over 6 million light years across; contrast this with the Milky Way

Milky Way

The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

, which is 100,000 light years across. It is 1.070 billion light-years away and about 80 times bigger than the Milky Way, with a light output 2 trillion times greater than our sun, as announced in July, 1990, by Juan M. Uson, Stephen P. Boughn, and Jeffrey R. Kuhn. This type of galaxy is called a cD-type

Type-cD galaxy

The type-cD galaxy is a galaxy morphology classification, a subtype of type-D giant elliptical galaxy, and has a large halo of stars. They can be found near the centres of some rich galaxy clusters...

 brightest cluster galaxy

Brightest cluster galaxy

Brightest cluster galaxy is defined as the brightest galaxy in a cluster of galaxies. BCGs include the most massive galaxies in the universe. They are generally elliptical galaxies which lie close to the geometric and kinematical center of their host galaxy cluster, hence at the bottom of the...

and may have grown to its large size by accreting nearby galaxies.

Sources

• Curious About Astronomy? , "What is the largest galaxy?", Cornell University