IC 1101
IC 1101 is a supergiant elliptical galaxy at the center of the Abell 2029 galaxy cluster. It is one of the largest known galaxies. Its halo extends about from its core. The core itself, which is the largest known core of any galaxy to date, hosts a supermassive black hole that is one of the largest black holes known. The galaxy is located from Earth. The galaxy was discovered on 19 June 1790, by the British astronomer William Herschel. Characteristics. The galaxy is classified as a supergiant elliptical (E) to lenticular (S0) and is the brightest galaxy in  A2029 (hence its other designation A2029-BCG; BCG meaning "brightest cluster galaxy"). The galaxy's morphological type is debated due to it possibly being shaped like a flat disc but only visible from Earth at its broadest dimensions. However, most lenticulars have sizes ranging from . IC 1101 is among the largest known galaxies, but there is debate in the astronomical literature about how to define the size of such a galaxy. Photographic plates of blue light from the galaxy (sampling stars excluding the diffuse halo) yield an effective radius (the radius within which half the light is emitted) of . The  galaxy has a very large halo of much lower intensity "diffuse light" extending to a radius of . The authors of the study identifying the halo conclude that IC 1101 is "possibly one of the largest and most luminous galaxies in the universe". Like most large galaxies, IC 1101 is populated by a number of metal-rich stars, some of which are seven billion years older than the Sun, making it appear golden yellow in color. It has a bright radio source at the center, which is likely associated with an ultramassive black hole in the mass range of , one of  the largest known black holes in the universe. A 2017 paper suggests that IC 1101 has the largest core size of any galaxy, with a core radius of around , making its core larger than the one observed in A2261-BCG. The core is also roughly an order of magnitude larger than the cores of other galaxies, such as NGC 4889 and NGC 1600. However, when examining large and diffuse galactic cores, caution must be taken, as various estimates may differ between the computer models used. As an example, Holmberg 15A was originally claimed to have the largest galactic core of  any galaxy but other studies proved otherwise.