Looking at these spiral galaxies glowing brightly against the dark, it's hard to imagine that they could be so easily missed — but they were right up until now, when an astronomical survey catalogued them as equal to the biggest and brightest galaxies ever seen. The galaxies pictured above, dubbed super spirals, were uncovered by the Sloan Digital Sky Survey. After astronomers combed through some of the distant data, they were surprised to see that some of the galaxies they were looking at were not close spiral galaxies of a normal size, but huge ones farther away. Lead author of the newly published paper in Astrophysical Journal, Patrick Ogle of the California Institute of Technology, described the discovery "as if we have just discovered a new land animal stomping around that is the size of an elephant but had shockingly gone unnoticed by zoologists".
Although they're quite comparable in their shape and their behaviour, they dwarf spiral galaxies as we know them. They have more than 10 times the mass of the Milky Way, anywhere from 8-14 times its brightness, and 30 times its star-formation ability. It's that incredible star-formation ability, though, that also has astronomers questioning everything they know about spiral galaxies.
Current theories say super spirals this size shouldn't be able to keep themselves together at all. As spiral galaxies grow, they pull in more and more surrounding gases to build stars. As they keep pulling, they eventually hit a point where they have too much surrounding gas and, instead of growing new stars, it extinguishes them. Yet, mysteriously, these super spirals seem to be almost unlimited in both how big they can get and how many stars they can build.
Super spiral galaxies / Sloan Digital Sky Survey