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Researchers discover a pristine triple galaxy from the Cosmic Dawn

by Kurt Kleiner
Dec 20 / 13

Researchers say they’ve observed a galaxy that dates to the Cosmic Dawn, when stars first began to form from the vast clouds of hydrogen and helium left over from the Big Bang.

P9-galaxy
The triple galaxy Himiko formed about 13 billion years ago. (Photo courtesy Richard Ellis).

“We’re looking back to a time when the universe was really very young,” says Richard Ellis, a member of the CIFAR Advisory Committee for the Cosmology & Gravity program, which attempts to explain the history and composition of our Universe. He is an astronomer at the California Institute of Technology.

Ellis and colleagues reported in the Astrophysical Journal that they have found a galaxy from about 13 billion years ago, when the Universe was only about 700 million years old. The galaxy is surrounded by a glowing cloud made up of only hydrogen and helium, the primordial elements of the early universe.

The researchers first discovered the galaxy using the Subaru Telescope on Mauna Kea in Hawaii, an 8.2 meter telescope uniquely capable of systematically surveying the deep night sky. Ellis and his fellow researchers used the telescope to search for star-forming galaxies at large redshift, indicating that they are at the distant reaches of our rapidly-expanding universe and therefore seen when the Universe was very young.

Amongst the sources they found was a surprisingly luminous spatially-extended “blob” which they christened “Himiko,” after a mythical Japanese queen. “Remarkably, Himiko is forming stars at a ferocious rate,” Ellis says, “about 100 solar masses a year. By contrast our own Milky Way produces only about one solar mass a year.”

To understand the origin of this intense activity, the researchers studied Himiko with the Hubble Space Telescope and found the system is actually composed of three different galaxies in the process of colliding. Most likely Himiko is being seen at a special time in its history and the triple merger is inducing a spectacular burst of activity that powers the surrounding glowing gas.

When Ellis and his colleagues examined the system with the new Atacama Large Millimeter/submillimeter Arrray (ALMA) in Chile’s Atacama Desert, they uncovered another surprise. Most galaxies forming new stars contain gas and dust polluted by carbon and other heavy elements created by the stars. But, using ALMA, Ellis and his colleagues were unable to find any evidence of carbon in Himiko, either in gaseous form or in dust.

The most likely explanation, Ellis says, is that Himiko is such a young galaxy that the stars haven’t yet had time to churn out the heavier elements that we find in older galaxies like our own.

The ALMA array is still under construction and its sensitivity is continuing to improve, so there is the prospect of finding more examples of primordial galaxies, he says.