Carbon is Surprisingly Abundant in an Early Galaxy

The James Webb Space Telescope (JWST) has once again found evidence that the early universe was a far more complex place than we thought. This time, it has detected the signature of carbon atoms present in a galaxy that formed just 350 million years after the Big Bang – one of the earliest galaxies ever observed.

“Earlier research suggested that carbon started to form in large quantities relatively late – about one billion years after the Big Bang,” said Kavli Institute Professor Roberto Maiolino. “But we’ve found that carbon formed much earlier – it might even be the oldest metal of all.”

‘Metal’ is the name astronomers give to any element heavier than hydrogen or helium, and seeing metals like carbon so early is a surprise. Carbon is, of course, one of the building blocks of life on Earth, but it also plays a role in galaxy and solar system formation. It is one of the materials that can accumulate in the protoplanetary disks around stars, snowballing to become planets, moons, and asteroids.

But astronomers weren’t expecting to see that process happening so early.

When the first stars (called population-III stars) were born, in an era of the universe known as Cosmic Dawn, the only plentiful elements around were hydrogen and helium. All heavier elements didn’t yet exist. They were only able to form later, inside the cores of stars, therefore wouldn’t be detectable until well after the deaths of the first stars.

Dying population-III stars that explode as supernovas throw their heavier elements out into the universe, allowing future populations of stars to develop rocky planets with more interesting chemistry.

The galaxy in question, named GS-z12, is thought to contain largely second generation stars, built from the remains of those first supernovas. Astronomers didn’t expect the building blocks of the galaxy to be carbon-rich:

“We were surprised to see carbon so early in the universe, since it was thought that the earliest stars produced much more oxygen than carbon,” said Maiolino. “We had thought that carbon was enriched much later, through entirely different processes, but the fact that it appears so early tells us that the very first stars may have operated very differently.”

JWST’s Near Infrared Spectrograph allowed astronomers to break down the light coming from the distant galaxy into its constituent parts, revealing all the different wavelengths present. Every element and chemical compound has its own signature when viewed via spectroscopy, and the signal for carbon was very strong. There was also a fainter signal for neon and oxygen, though those remain tentative detections for the moment.

How carbon emerged before oxygen is an open question, but one hypothesis proposes that scientists now need to revisit their models of population-III star supernovas. If these supernovas occurred with less energy than previously thought, then they would scatter carbon from the stars’ outer shells, while most of the oxygen present would be captured within the event horizon as the stars collapsed into black holes.

Regardless of how it happened, there is now a strong case for heavy elements early in the universe – far earlier than anyone guessed. JWST is revealing unexpected details about the first galaxies that will ultimately make scientists’ predictions about the evolution of the universe far more robust. And perhaps most significantly, it also tells us about the very first step towards creating life.

“These observations tell us that carbon can be enriched quickly in the early universe,” said Francesco D’Eugenio of the Kavli Institute. “And because carbon is fundamental to life as we know it, it’s not necessarily true that life must have evolved much later in the universe. Perhaps life emerged much earlier – although if there’s life elsewhere in the universe, it might have evolved very differently than it did here on Earth.”

Learn More:

“Earliest detection of metal challenges what we know about the first galaxies.” University of Cambridge.

D’Eugenio et al. “JADES: Carbon enrichment 350 Myr after the Big Bang in a gas-rich galaxy.” ArXiv preprint (accepted to Astronomy & Astrophysics).

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