Infant Galaxies Merge Near 'Cosmic Dawn' of the Universe

Astronomers have made a startling find. They've discovered a far-flung trio of primitive galaxies within an enormous cloud of primordial gas nearly 13 billion light-years from Earth. The rare discovery reveals a little bit more about the process of galaxy formation in the early Universe.

"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," said Richard Ellis, one of the researchers, in a news release. "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."

The system was actually first detected in 2009. Astronomers first believed that it was a bubble of hot, ionized gas. Dubbed Himiko, the system is nearly 10 times larger than typical galaxies of that era and comparable to our own Milky Way. Now, researchers have found that Himiko is not a single galaxy but is, instead, three distinct, bright sources.

This region is undergoing a bout of star formation, which means that it should be brimming with heavy elements such as carbon, silicon and oxygen. These elements are forged in the nuclear furnaces of massive, short-lived stars like those bursting into life inside the three galaxies detected by Hubble. Yet it seems like this isn't the case.

"Surprisingly, observations with ALMA revealed a complete absence of the signal from carbon, which is rapidly synthesized in young stars," said Masami Ouchi, one of the researchers, in a news release. "Give the sensitivity of ALMA, this is truly remarkable. Exactly how this intense activity can be reconciled with the primitive chemical composition of Himiko is quite puzzling."

It's possible that a large fraction of the gas in Himiko could be primordial, a mixture of the light elements hydrogen and helium, which were created in the Big Bang. This, in turn, would make the system and landmark discovery and would signal the detection of a primordial galaxy seen during its formation.

"Astronomers are usually excited when a signal from an object is detected," said Ellis in a news release. "But, in this case, it's the absence of a signal from heavy elements that is the most exciting result!"

The findings are published in The Astrophysical Journal.