“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. […]
But the largest and most massive galaxies aren’t spirals, but supergiant ellipticals, like NGC 4874 in the Coma Cluster.”
From our vantage point within the Milky Way, it sure does appear impressive. Hundreds of billions of stars shine in our own cosmic backyard, with our galaxy spanning a whopping 100,000 light years from end-to-end. Yet not only is that small compared to our nearest large neighbor, Andromeda, but it’s not even 20% as large as the largest spiral galaxies we find. While tidal disruption might create the largest spiral galaxies, we have giant ellipticals that are many times larger than a spiral will ever achieve. Some of the biggest ones of all are found at the centers of massive galaxy clusters, but in the scheme of the entire observable Universe, only one galaxy can truly be the largest.