Astronomers finally measure the full size of the largest known galaxy
Astronomers have used ultra-deep imaging to measure the full extent of the galaxy IC 1101, confirming it as the largest known galaxy at approximately 1.7 million light-years across. The study helps clarify how brightest cluster galaxies grow through the absorption of smaller systems.
Why it matters
This discovery provides critical data for understanding the evolution of large-scale structures in the universe.
edited by Gaby Clark , reviewed by Robert Egan
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Add as preferred source Comparison of color-composite images of IC 1101 obtained from different imaging surveys. From left to right: SDSS DR16, the DESI Legacy Imaging Surveys DR9 based on DECaLS imaging, and the INT/WFC data presented in this work. Credit: Carlos Marrero-de la Rosa et al. (2026). DOI: https://doi.org/10.48550/arXiv.2607.15340 Researchers have obtained the deepest images ever taken of IC 1101, allowing them to identify the galaxy's outer edge for the first time. The observations confirm it as the largest known galaxy, spanning roughly 520 kiloparsecs, or about 1.7 million light-years, and containing an estimated 3.4 trillion solar masses in stars. The paper was posted to the arXiv preprint server on July 16.
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