New York, March 18: In archived NASA data, astronomers have discovered a class of galactic leviathans called "super spiral" galaxies that dwarf our own galaxy, the Milky Way, and compete in size and brightness with the largest galaxies in the universe.
Super spirals have long hidden in plain sight by mimicking the appearance of typical spiral galaxies.
"We have found a previously unrecognised class of spiral galaxies that are as luminous and massive as the biggest, brightest galaxies we know of," said study lead author Patrick Ogle, astrophysicist at the Infrared Processing and Analysis Center (IPAC) at the California Institute of Technology in Pasadena, US.
The findings were published in The Astrophysical Journal.
"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," Ogle added.
Ogle and colleagues chanced upon super spirals as they searched for extremely luminous, massive galaxies in the NASA/IPAC Extragalactic Database (NED), an online repository containing information on over 100 million galaxies.
"Remarkably, the finding of super spiral galaxies came out of purely analysing the contents of the NASA/IPAC Extragalactic Database, thus reaping the benefits of the careful, systematic merging of data from many sources on the same galaxies," study co-author George Helou, executive director of IPAC, said.
The researchers expected that humongous, mature galaxies called ellipticals -- so named for their football-like shapes -- would dominate their search within NED for the most luminous galaxies. But a tremendous surprise lay in store for the scientists.
In a sample of approximately 800,000 galaxies no more than 3.5 billion light-years from Earth, 53 of the brightest galaxies intriguingly had a spiral, rather than elliptical, shape.
The researchers double-checked the distances to the spiral galaxies and saw that none were nearby -- even the closest lay some 1.2 billion light-years away. With the correct distance estimates in hand, the stunning properties of this newfound batch of whirlpool-shaped galaxies came to light.
Super spirals can shine with anywhere from eight to 14 times the brightness of the Milky Way. They possess as much as 10 times our galaxy's mass.
Their gleaming, starry disks stretch from twice to even four times the width of the Milky Way galaxy's approximately 100,000 light-year-wide disk, with the largest super spiral spanning a whopping 440,000 light-years.
Super spirals also give off copious ultraviolet and mid-infrared light, signifying a breakneck pace of churning out new stars. Their star formation rate is as high as 30 times that of our own run-of-the-mill galaxy.
"Super spirals could fundamentally change our understanding of the formation and evolution of the most massive galaxies," Ogle said.
"We have much to learn from these newly identified, galactic leviathans," Ogle noted.