Scientists believe they have figured out why a mysterious giant ball of gas in the distant universe glows so brightly, and the answers may help explain how galaxies are formed.
Lyman-alpha Blobs, or LABs, are faraway clouds of hydrogen gas that can span hundreds of thousands of light-years and emit bright ultraviolet light.
Scientists don't know what causes LABs to shine so brightly, or even how they came to be, although there have been many competing theories.
But we're one step closer to understanding the origins of these mysterious space blobs — and possibly the origins of galaxy formation itself — thanks to a study set to be published in the Astrophysical Journal.
Solving a 15-year-old mystery
"For a long time, the origin of the extended Lyman-alpha light has been controversial. But with the combination of new observations and cutting-edge simulations, we think we have solved a 15-year-old mystery," lead author Jim Geach, a research fellow at the University of Hertfordshire's Centre for Astrophysics Research in the U.K., said in a statement.
Geach and other members of an international team of scientists set their sights on one of the biggest-known LABs.
Called LAB-1, it is so far away from Earth that it took 11.5 billion years for its light to reach us, which means when we look at it, we're peering into the early history of the universe.
Discovered in 2000, images taken from powerful telescopes show that LAB-1 emits a shimmering emerald green colour.
Canadian scientist Scott Chapman is a member of Geach's international team who led the initial discovery of the blob's luminescent nature 15 years ago when he was doing post-doctoral work using the James Clerk Maxwell Telescope in Hawaii.
"The field of distant galaxies in the universe was just starting to open up," Chapman, now a physics professor at Dalhousie University in Halifax, told CBC News.
"I had an observing run on this telescope… and I pointed it at this object and it turned out to be an incredibly bright galaxy with these infra-red wavelengths."
Since then, scientists have proposed numerous theories about what could possibly powering all that glowing gas: cool gas being pulled in by the blob's powerful gravity, perhaps, or a black hole engulfing matter from within the blob itself.
But it wasn't until now — using the Atacama Large Millimeter/submillimeter Array telescope and the Very Large Telescope at the European Southern Observatory in Chile — that astronomers have been able to get a closer look at the green space blob.
Turns out, the pretty light show is all star power.
At the heart of LAB-1, scientists pinpointed two large galaxies, forming stars at a rate over 100 times that of the Milky Way and lighting up the hydrogen gas that surrounds them.
'What's exciting about these blobs is that we are getting a rare glimpse of what's happening around these young, growing galaxies.' - Jim Geach, astrophysicist
"Think of a streetlight on a foggy night — you see the diffuse glow because light is scattering off the tiny water droplets. A similar thing is happening here, except the streetlight is an intensely star-forming galaxy and the fog is a huge cloud of intergalactic gas," Geach said.
The findings are no surprise to Chapman. He always suspected star formation was powering the luminous blob.
"It's very hard to get that level of emission from anything else other than star formation. People who work in that field have always felt that any other explanation is a little contrived," he said.
"But certainly in 2000, people were incredulous that any galaxy could be forming stars at that incredible rate because they'd never been seen before."
Snapshot in time
And what's more, the two big galaxies are at the centre of a swarm of smaller ones in what appears to be the early phases of the formation of a massive galaxy cluster.
Scientists believe some of the universe's most massive galaxies form in LABs and each discovery brings us closer to understanding how and why that happens.
"What's exciting about these blobs is that we are getting a rare glimpse of what's happening around these young, growing galaxies," Geach said.
"Lyman-alpha Blob-1 is the site of formation of a massive elliptical galaxy that will one day be the heart of a giant cluster. We are seeing a snapshot of the assembly of that galaxy 11.5 billion years ago," Geach said.