April 24, 2021

The galaxy is classified as a supergiant elliptical (E) to lenticular (S0)[3] and is the brightest galaxy in A2029 (hence its other designation A2029-BCG; BCG meaning brightest cluster galaxy).[6][7] 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 15 to 37 kpc (50 to 120 thousand ly).[8][specify]

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 65 ± 12 kpc (212 ± 39 thousand ly).[4] The galaxy has a very large halo of much lower intensity “diffuse light” extending to a radius of 600 kpc (2 million ly).[9] 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”.[9]

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 40–100 billion M☉, one of the largest known black holes in the universe.[10][11]

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