In this illustration, green indicates ionized oxygen, while purple shows the distribution of ionized hydrogen. (NAOJ)

Oxygen has been detected in a galaxy from long, long ago and far, far away. 13.1 billion light-years away, to be exact.

This galaxy — which we're observing as it was just 700 million years after the birth of the universe — shows the oldest signs of oxygen scientists have ever seen. That's a big deal: In the immediate aftermath of the Big Bang, only the lightest elements — helium, lithium and hydrogen — existed. Heavier elements, such as carbon and oxygen, are necessary for the formation of life as we know it. But these elements didn't form until the first stars had aged enough to produce them by way of fusion.

The new research on galaxy SXDF-NB1006-2, published Thursday in the journal Science, helps get us closer to pinpointing the origin of these life-giving molecules.

For starters, it could help us get a handle on the dark ages. Not the time period on Earth, but the one that happened on a universal scale. After the Big Bang, everything was hot and exciting. But after a few hundred thousand years, things cooled and calmed down. The gas that had held particles with electric charges became neutral hydrogen. Enter the dark ages, when the universe had nothing to do but slowly bring its neutral hydrogen gas into gravity-gathered clumps.

Fast-forward a few hundred million years, and you finally get enough hydrogen in one place to form the very first star. Stars ionized the gas around them — meaning they made the neutral particles charged again — in a phenomenon known as cosmic reonization. Eventually the universe hit a critical mass of hydrogen-processing stars, and it started to look like the incredible star factory we know and love. We can't actually see the birth of these first stars, because all that hydrogen was pretty opaque, so scientists are always trying to push further and further back in time.


A color composite image of a portion of the Subaru XMM-Newton Deep Survey Field. The red galaxy at the center of the image is the most distant galaxy, SXDF-NB1006-2. (NAOJ)

When it was discovered in 2012, SXDF-NB1006-2 was the oldest, most distant galaxy ever observed. That record has since been broken several times, but it still gets us about as close to the dark ages as we can get. The galaxy was first spotted by the Subaru Telescope because of the glow of ionized hydrogen being given off by its young stars, but follow-ups with the Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope revealed the glow of ionized oxygen as well.

The galaxy doesn't contain much oxygen — just around 10 percent of the oxygen found in our own sun — but that's to be expected.

"The small abundance is expected because the Universe was still young and had a short history of star formation at that time," study author Naoki Yoshida of the University of Tokyo said in a statement. "In fact, our simulation predicted an abundance ten times smaller than the Sun. But we have another, unexpected, result: a very small amount of dust."

SXDF-NB1006-2's oxygen content could only be supported by the existence of several stars over a dozen times more massive than the sun. The lack of dust hasn't been explained, but it may have allowed these stars to shine their ultraviolet light out into the void, helping them push reionization forward.

"SXDF-NB1006-2 would be a prototype of the light sources responsible for the cosmic reionization," study author Akio Inoue of Osaka Sangyo University said in a statement.

Studying galaxies like this one in even higher resolutions may finally illuminate the dark ages of our universe.

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