IC 1101 galaxy size measured at 1.7 million light-years

An international research team led by the Instituto de Astrofísica de Canarias (IAC) has determined the precise size of IC 1101, the largest known galaxy in the universe. Published in Astronomy & Astrophysics, the study confirms that the galaxy's main body reaches a diameter of approximately 1.7 million light-years, making it about ten times larger than the Milky Way.

Located at the center of the Abell 2029 galaxy cluster roughly one billion light-years from Earth, IC 1101 had long been recognized as an extreme galaxy, but its physical boundaries remained unclear due to the difficulty of distinguishing its outer edges from the surrounding cluster stars. Researchers utilized ultra-deep images from the Isaac Newton Telescope (INT) at the Roque de los Muchachos Observatory in La Palma to observe extremely faint regions.

By analyzing simultaneous changes in brightness, color, shape, and stellar mass distribution, the team identified a transition at a radius of approximately 850,000 light-years from the center. At this point, the stellar orientation changes and the structure becomes more rounded, marking the boundary of the galaxy's main body.