We’ve discovered some behemoths, but one outclasses them all.
“There is always a heavy demand for fresh mediocrity. In every generation the least cultivated taste has the largest appetite.” –Paul Gauguin
Our Milky Way contains some 400 billion stars, spanning 100,000 light years in diameter.
Yet compared to other galaxies, it’s not even especially large.
In our own local group, the Andromeda galaxy is significantly larger, reaching 220,000 light years across.
Interacting spiral galaxies can have their arms greatly extended and disrupted, with NGC 6872 spanning 522,000 light years from tip-to-tip.
Ultra-low surface brightness galaxies can see their stars extend even farther, with Malin 1 reaching 650,000 light years across.
Unsurprisingly, a disrupted low surface brightness galaxy, UGC 2885, is the largest spiral known at 832,000 light years.
Hydrogen gas and dark matter halos can continue beyond the stars, like in NGC 262, extending over 1,000,000 light years.
But the largest and most massive galaxies aren’t spirals, but supergiant ellipticals, like NGC 4874 in the Coma Cluster.
Coma has two enormous core ellipticals, with the even larger NGC 4889 reaching 1.3 million light years in diameter.
Even larger ones reside inside more massive galaxy clusters, like the brightest galaxy in the Phoenix cluster, at 2.2 million light years.
Still, IC 1101 beats them all, extending for 5.5 million light years.
Periodic star formation, mergers, and gravitational growth over time inevitably lead to these cosmic behemoths.
Mostly Mute Monday tells the scientific story of an astronomical object, class or phenomenon in visuals, images and no more than 200 words.Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.