A group of astronomers say they've discovered the largest known spiral galaxy — five times the size of the Milky Way — after studying data from NASA's Galaxy Evolution Explorer (GALEX) satellite.
Astronomers from Chile, Brazil and the U.S. had been using the GALEX on loan at the California Institute of Technology in Pasadena, Calif. Through it, they found a galaxy that is five times the size of our own galaxy, the Milky Way, and more than 522,000 light-years in width.
The findings were presented at the American Astronomical Society meeting on Jan. 10.
Rafael Eufrasio, a research assistant at NASA's Goddard Space Flight Centre in Maryland, said the team was not trying to discover a new galaxy. "It just came as a gift," he told BBC News.
NGC 6872 is about 212 million light-years away in the constellation Pavo in the southern sky.
Eufrasio says NGC 6872 has an unusual size, which is likely due to its interaction with a much smaller galaxy named IC4970.
Astronomers believe large galaxies, like our own, spun out on their own after merging with and acquiring elements from other smaller systems over billions of years.
The scientists examined this new galaxy further and found the youngest stars were in the outer reaches of its massive spiral arms, while the older ones were in the centre.
That suggests a wave of star formation set off by a collision with IC 4970 — typical of a galactic encounter.
"The galaxy that collided with [NGC 6872] splashed stars all over the place [as far as] 500,000 light-years away," noted Eufrasio.
Discovery of NGC 6872 helps astronomers learn more about how galaxies can be altered by collisions.
"It shows the evolution of galaxies in the larger context of the universe," said Eufrasio.