IC 1101 Confirmed as Largest Known Galaxy at 1.7 Million Light‑Years Across

Astronomers led by Carlos Marrero‑de la Rosa of the Instituto de Astrofísica de Canarias used ultra‑deep images from the Isaac Newton Telescope in the United Kingdom to map the outermost light of the giant elliptical galaxy IC 1101. The analysis identified the galaxy’s boundary at roughly 520 kiloparsecs, or about 1.7 million light‑years in diameter, establishing IC 1101 as the largest galaxy currently known.

IC 1101 resides at the centre of the Abell 2029 galaxy cluster, about one billion light‑years from Earth. The new measurement refines earlier estimates that placed its size near 607 kiloparsecs and provides insight into the hierarchical growth of Brightest Cluster Galaxies, which expand by accreting smaller galaxies and dark‑matter halos over billions of years.