IC 1101 confirmed as the biggest known galaxy, spanning 1.7 million light-years

Using the longest-exposure photographs ever taken of IC 1101, captured in 2022 by the Isaac Newton Telescope at the Roque de los Muchachos Observatory, scientists have calculated the galaxy’s span to be roughly 520 kiloparsecs—about 1.7 million light-years, which would line up 17 Milky Ways side by side. The team estimates the galaxy contains about 3.4 trillion times the Sun’s mass in stars. Visible, tail-like structures extending from its edges indicate ongoing mergers with smaller galaxies, a process the researchers label galactic cannibalism.

Located more than a billion light-years distant in the heart of the Abell 2029 cluster, IC 1101 is the brightest cluster galaxy of its group. Carlos Marrero de la Rosa of the Instituto de Astrofísica de Canarias said the object illustrates how repeated accretion can produce a galaxy of unprecedented scale, hinting at what massive galaxies may become in the future.