via reddit

Wikipedia: IC 1101 is a supergiant elliptical galaxy at the center of the Abell 2029 galaxy cluster. It is 1.07 billion light years away in the constellation of Virgo and is classified as a cD class of galaxy. It was discovered in June 19, 1790 by William Herschel. The galaxy has a diameter of approximately 6 million light years, which makes it currently (as of 2013) the largest known galaxy in terms of breadth.[2] It is the central galaxy of a massive cluster containing a mass (mostly dark matter) of roughly 100 trillion stars.[3][4] Being more than 50 times the size of the Milky Way and 2000 times as massive, if it were in place of our galaxy, it would swallow up the Large Magellanic Cloud, Small Magellanic Cloud, Andromeda Galaxy, and Triangulum Galaxy. IC 1101 owes its size to many collisions of much smaller galaxies about the size of the Milky Way and Andromeda galaxies.