IC 1101 identified as the largest known galaxy with 1.7 million light-year diameter

Astronomers have determined that IC 1101 is the largest known galaxy, measuring approximately 1.7 million light-years in diameter. A research team led by astrophysicist Carlos Marrero de la Rosa achieved this measurement by utilizing the deepest images of the galaxy to date, captured in 2022 using the 2.5-meter Isaac Newton Telescope at the Roque de los Muchachos Observatory in Spain.

Determining the exact boundaries of IC 1101 has historically been difficult because galaxies lack distinct edges and their outer stars blend into the light of surrounding clusters. To isolate the galaxy's true size, researchers had to meticulously remove light interference from the telescope, the atmosphere, and foreground stars.

By analyzing the cleaned images, scientists identified the main stellar area extending about 260 kiloparsecs from the center. This diameter is roughly twenty times larger than the stellar disk of the Milky Way. If placed in our local neighborhood, IC 1101 would nearly span the entire distance between the Milky Way and the Andromeda galaxy. The galaxy is located at the center of the Abell 2029 galaxy cluster.