NASA’s Webb Telescope detects farthest known carbon in space

Astronomers have discovered the most distant known carbon in the universe, dating back just 350 million years after the Big Bang. The finding — made by NASA’s Webb Space Telescope — used infrared observations from its current Advanced Deep Extragalactic Survey to identify carbon in a baby galaxy that formed shortly after the dawn of time.

The findings are likely to force cosmologists and theorists to rethink much of what they know about the chemical enrichment of our cosmos.

In an article accepted for publication in a journal Astronomy and astrophysics, an international team led by astronomers from the University of Cambridge in the UK, details their observations of this early galaxy, known as GS-z12. It lies at a redshift greater than 12, near the cosmic dawn.

This is not only the earliest confirmed detection of carbon, but also the first confirmed detection of any chemical element other than the primordial elements produced by the Big Bang (hydrogen, helium and traces of lithium), Francesco D’Eugenio, lead author of the paper and an astrophysicist at the University of Cambridge, told me by e-mail.

Finding this carbon so early in cosmic history could also mean that life may have started somewhere out there even earlier than previously thought.

The discovery also challenges our models of chemical evolution, says D’Eugenio. We didn’t expect to see such a high ratio of carbon to oxygen until much later in the history of the universe, he says. Our discovery therefore points to new and unexpected channels of chemical enrichment in the early universe, says D’Eugenio.

Due to the extraordinary faintness of such distant galaxies, the team was only able to detect the carbon after about 65 hours of observation using near-infrared spectroscopy.

Astronomers use spectroscopy to study the absorption and emission of light and other radiation by matter. Each element has its own chemical signature that appears in the spectra of the celestial target, which in this case allowed the surprising identification of carbon at such early times.

How did this carbon come about?

The Big Bang produced only hydrogen, helium and traces of lithium, D’Eugenio says. Therefore, this carbon—and all carbon in the universe—must have been produced inside stars, he says. Some of the carbon is formed inside short-lived massive stars and some in long-lived low-mass stars, D’Eugenio says.

Carbon via Supernovae

In GS-z12, which is only about 50 million solar masses, we can rule out the second scenario because the universe was so young that low-mass stars haven’t had enough time to contribute significant amounts of carbon, D’Eugenio says. That means it was made in massive stars, he says. However, the carbon-to-oxygen ratio we see in GS-z12 does not match the products of known massive stars, D’Eugenio says. This is why we suspect that this detected carbon could have been produced in more exotic types of massive stars, such as Population III stars, he says.

Population III stars are the theoretical population of the very first stars in the universe.

According to some models, when these oldest stars exploded as supernovae, they may have released less energy than originally expected, notes the University of Cambridge. In this case, the carbon, which was in the outer shell of stars and was less gravitationally bound than oxygen, the university says. So that carbon could escape more easily and spread throughout the galaxy, while large amounts of oxygen fell back and collapsed into the black hole, the university reports.

Would this carbon be the result of a population III supernova?

We don’t know for sure what kind of star produced this carbon, D’Eugenio says. However, given the really short time available for stars to evolve, it must have come from supernova explosions caused by the death of massive stars, D’Eugenio says. Evidence from the local universe up to one billion years after the Big Bang shows that the ratio of carbon to oxygen produced by supernovae is much lower than what we see in this galaxy, he says.

Carbon to oxygen ratios

Explaining the high carbon-to-oxygen ratio observed in GS-z12 is difficult in the current framework, D’Eugenio says. In this context, there are some theoretical scenarios in which population III supernovae provide high carbon-to-oxygen ratios; that would be a suitable scenario, but it needs to be confirmed, he says.

As for the detected carbon?

It was produced in one of the inner envelopes of a massive helium-burning star as it was about to go supernova, D’Eugenio says. When a star went supernova, its carbon-enriched gas flowed back into the galaxy, he says.

And that’s when it became detectable.

Such early supernovae and their byproducts represent the first steps in cosmic chemical enrichment. Over billions of years, this chemical evolution resulted in a group of galaxies like our Milky Way; chemically rich and — at least on this planet — teeming with carbon-based life.