IC 1101
Nestled within the heart of the Abell 2029 galaxy cluster, within the constellation Virgo, resides IC 1101—a colossal galaxy that renders our Milky Way a mere speck of cosmic dust. Initially discovered on June 19, 1790, by the renowned British astronomer William Herschel, IC 1101 still holds its position as one of the largest galaxies known to humanity.
Unveiling IC 1101, The Largest Galaxy?
In the epoch of its discovery, back in 1790, these cosmic entities were perceived as nebulous formations confined within the bounds of our own Milky Way. It wasn't until 1920, when Edwin Hubble revolutionized our understanding of the universe by demonstrating the extragalactic nature of Andromeda through the study of Cepheid variable stars, that the concept of galaxies beyond our own began to take shape.
Among this vast cosmic tapestry, IC 1101 stands as a pinnacle of intrigue. Classified as a supergiant elliptical galaxy, it boasts a staggering diameter ranging from 400,000 to 550,000 light-years, firmly securing its place as one of the largest galaxies ever charted. For decades, it reigned as the unrivalled titan of the cosmos.*
Expanding across approximately 4 million light-years, IC 1101 casts its vast influence, extending its diffuse halo up to 2 million light-years from its core. Astronomers speculate that the galaxy's immense size stems from the amalgamation of numerous smaller galaxies—a theory substantiated by the dearth of interstellar matter, resulting in a diminished rate of star formation.
The precise distance of IC 1101 from Earth remains elusive, with varying calculations yielding differing results. Initial estimations in 1980 placed it approximately 850 million light-years away, yet recent assessments suggest a distance of 1.2 billion light-years.
While pinpointing the exact number of stars within IC 1101 proves challenging due to its distance, astronomers speculate that it harbours around 100 trillion stars, contributing to its dazzling luminosity. However, the scarcity of interstellar matter implies a subdued rate of stellar birth, endowing the galaxy with predominantly aged, metal-rich stars, casting IC 1101 in its distinctive golden hue.
The galaxy's nucleus ranks among the largest ever observed, if not the largest, boasting an apparent size of 2.77 arcseconds or 13,700 light-years. Observable radio bursts emanating from its core suggest the presence of a supermassive black hole—common among large galaxies—lurking within.
The mass of this black hole remains a matter of debate, with estimates ranging between 50 and 70 billion or 40 to 100 solar masses, contingent upon the method of calculation employed. Regardless, it stands as one of the most massive black holes ever detected.
*Despite reigning as the largest known galaxy for decades, IC 1101 relinquished its crown in February 2022 with the unveiling of a colossal radio galaxy christened Alcyoneus. Alcyoneus, situated within the Lynx constellation approximately 3.5 billion light-years away, spans an astounding 16 million light-years across, eclipsing even the grandeur of IC 1101.