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Found! Oldest galaxy pile-up

Astronomers have discovered the most distant galactic collisions yet, a cluster of early galaxies caught merging into one giant galaxy when the universe was just a toddler.

The galactic 'proto-cluster', named LBG-2377, is a whopping 11.4 billion light-years away and in the past.

It provides a window into a time well after the universe inflated and spread matter far and wide.

But it was still a time when all of that matter was coalescing to make the clusters and super-clusters of galaxies that collectively create the cobwebby structure of matter in the modern universe.

The team used the volcano-top Keck Telescope in Hawaii to capture the image of the galaxies in the act of coming together at about two billion years after the Big Bang.

The discovery was originally part of a broader survey of distant galaxies.

"This particular system showed up as a particularly bright one," says Dr Jeff Cooke, a postdoctoral researcher at the University of California at Irvine (UCI).

Cooke and his colleagues publish their discovery in the online astrophysics bulletin astro-ph, accessible via the arXiv website.

To be so bright at such a distance, LBG-2377 must be about 10 times the mass of the Milky Way, say the researchers.

They gleaned the number of galaxies involved in the merger from LBG-2377's spectra of light, which contain multiple galactic signals.

Equally important is the fact that the galaxies have been caught in the act of firing up loads of young stars that are very bright in ultraviolet light.

"It wasn't at all what I expected," Cooke says. "The event is so violent and catastrophic and they are creating so many new stars" that it shines far brighter than any other galaxies or clusters of galaxies at such a distance.

"It's definitely the furthest merging galaxy cluster."

How do galaxy's cluster?

Scientists think all galaxy clusters form in the same way; they gather in growing groups over time and sometimes merge to form giant galaxies.

Watching this happen at all ages of the universe helps to test theories of how the universe evolved.

Galaxy clusters closer to earth can contain more than 1000 galaxies. Our own galaxy belongs to what's called the Local Group, which contains at least 35 galaxies, most of which are very dim.

"We believe LBG-2377 is a seed that eventually will grow into a massive galaxy cluster," says Assistant Professor James Bullock, one of the study's co-authors and the director of the Center for Cosmology at UCI.

Eager to learn more

Other astronomers agree and are anxious to learn more about LBG-2377.

"It's very rare," says astronomer Alice Shapley, an assistant professor at Princeton University.

"If you look at the spectra of this object and its picture it breaks up into a lot of pieces."

But looking at LBG-2377 in UV and visible light is not telling the whole story, Shapley says.

To properly compare this ancient merger to modern mergers and galaxies, scientists need to study it in other wavelengths.

This way the light of older stars, which don't emit much UV light, can also be accounted for.

"It will be interesting to use the Hubble Space Telescope to look at it," says Shapley.