The far-flung primitive triplet galaxies are nestled inside an enormous blob of primordial gas, they reported Thursday.
"This exceedingly rare triple system, seen when the Universe was only 800 million years old, provides important insights into the earliest stages of galaxy formation during a period known as 'Cosmic Dawn,' when the universe was first bathed in starlight," Richard Ellis, a professor of astronomy at the California Institute of Technology, said. "Even more interesting, these galaxies appear poised to merge into a single massive galaxy, which could eventually evolve into something akin to the Milky Way."
When first detected in 2009, the galaxies were thought to be one giant galaxy, nearly 10 times larger than typical galaxies of that age, that astronomers dubbed Himiko after a legendary queen of ancient Japan.
"The new observations revealed that, rather than a single galaxy, Himiko harbors three distinct, bright sources, whose intense star formation is heating and ionizing this giant cloud of gas," said Masami Ouchi, a University of Tokyo researcher who led the international team of astronomers from Japan and the United States.
A large fraction of the gas in Himiko could be primordial, they researchers said, a mixture of the light elements hydrogen and helium created in the Big Bang.
If confirmed, this would be a landmark discovery signaling the detection of a primordial galaxy seen during its formation, they said.