IC 1101 confirmed as the largest known galaxy

An international team of astronomers, led by Carlos Marrero‑de la Rosa of the Instituto de Astrofísica de Canarias, used the Isaac Newton Telescope to map the full extent of the galaxy IC 1101. By modelling and subtracting the light of more than 250 foreground stars, they measured a radius of 260 kiloparsecs, giving the galaxy a total diameter of about 520 kiloparsecs (≈1.7 million light‑years). This makes IC 1101 roughly 17 times wider than the Milky Way and gives it a stellar mass of about 3.4 trillion solar masses, exceeding the Milky Way’s total mass.

IC 1101 sits at the centre of the Abell 2029 galaxy supercluster. The study notes that the galaxy is still growing, with faint asymmetric stellar structures beyond its main edge indicating ongoing accretion of smaller galaxies. Its core also hosts an ultra‑massive black hole estimated to be several hundred billion times the mass of the Sun, placing it among the largest known black holes.

These findings reinforce IC 1101’s status as the largest known galaxy and provide new insight into the formation and evolution of the most massive galactic systems in the universe.