A new class of "super spiral" galaxies has been found hiding in plain sight. While the new spiral galaxies appear to be nearby, they are actually quite far away, and went unnoticed for many years until now.
Astronomers from the California Institute of Technology discovered this new galactic type in archived data. They call them "superluminous spiral galaxies," as they can have up to 10 times the mass of the Milky Way and eight to 14 times the brightness of our own galaxy.
The results, available in a paper online to be published in The Astrophysical Journal, show that these objects are not just heavy and bright, but also large. The Milky Way's diameter is about 100,000 light-years, while the largest "super spiral" is over 400,000 light-years across. They are also a lot more active, producing up to 65 solar masses worth of new stars every year.
"We have found a previously unrecognized class of spiral galaxies that are as luminous and massive as the biggest, brightest galaxies we know of," said Patrick Ogle, an astrophysicist at the Infrared Processing and Analysis Center (IPAC) and lead author of the paper, in a statement. "It's 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."
Another super spiral is shown here in an image taken by the Sloan Digital Sky Survey. SDSS
The discovery was possible thanks to the NASA/IPAC Extragalactic Database (NED), an online database containing more than 100 million galaxies. The team looked at a smaller sample of nearby very bright galaxies, up to 3.5 billion light-years away, and among those 1,616 galaxies, they discovered 53 spirals that didn’t fit into any expected category.
"Remarkably, the finding of super spiral galaxies came out of purely analyzing the contents of the NASA/IPAC Extragalactic Database [NED], thus reaping the benefits of the careful, systematic merging of data from many sources on the same galaxies," said George Helou, a study co-author and the executive director of IPAC. "NED is surely holding many more such nuggets of information, and it is up to us scientists to ask the right questions to bring them out."
This discovery is important in expanding our understanding of galaxy evolution, and how the largest and brightest galaxies in the universe came to form.
"Super spirals could fundamentally change our understanding of the formation and evolution of the most massive galaxies," said Ogle. "We have much to learn from these newly identified, galactic leviathans."