Deep in outer space, about 11 billion light years from Earth, astronomers have observed the colossal merger of two galaxies, an intergalactic mash-up that is birthing 2,000 new stars each year and has helped scientists better understand an important cosmic mystery.

The massive galaxy, about 10 times the size of our Milky Way, was initially spotted by the now-retired Hershel infrared space observatory, and then followed up by observations from NASA's Hubble and Chandra space telescopes and from-Earth observations taken at the Keck Observatory.

The 400-billion-star mega-galaxy, which researchers have named HXMM01, is the "brightest, most luminous and most gas-rich submillimeter-bright galaxy known," according to researchers at University of California, Irvine, where the research was led.

The discovery helps scientist better understand how giant elliptical galaxies developed quickly in the early universe and why the massive galaxies stopped producing stars soon after.

The answer, they're finding, lies in hydrogen.

As the two smaller galaxies collide, they consumed vast amounts of hydrogen, one of the crucial building blocks of space matter, quickly using up the gas.

Other theories suggest that massive black holes in the center of the galaxies blow strong winds that dispersed the gas. But cosmologist Asantha Cooray, the UC Irvine team's leader, said that they and colleagues across the globe found definitive proof that cosmic mergers and the resulting highly efficient consumption of gas for stars are causing the quick burnout.

"These galaxies entered a feeding frenzy that would quickly exhaust the food supply in the following hundreds of million years and lead to the new galaxy's slow starvation for the rest of its life," Hai Fu, a UC Irvine postdoctoral scholar, said in a press statement. 

The find also clarifies an old question regarding the formation of the universe.

When the universe was just 3 billion years old, it contained large, red elliptical galaxies populated with old stars. Scientists have long wondered whether those large elliptical galaxies were built by the merger of lots of small galaxies, or by the quick collision of large galaxies.

The discovery of HXMM01, however, leads scientists to believe the latter.

"Finding this type of galaxy is as important as the discovery of the archaeopteryx was in understanding dinosaurs' evolution into birds, because they were both caught at a critical transitional phase," said Fu.  

The research is published in the journal Nature.