The James Webb Space Telescope (JWST) has found new evidence that the early universe was a much 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.
“Previous research suggested that carbon started forming in large quantities relatively late – about a billion years after the Big Bang,” says Professor Roberto Maiolino of the Kavli Institute. “But we discovered that carbon was formed much earlier – it could even be the oldest metal of all.”
‘Metal’ is the name astronomers give to any element heavier than hydrogen or helium, and it’s a surprise to see metals like carbon so early. Carbon is of course one of the building blocks of life on Earth, but it also plays a role in the formation of galaxies and solar systems. It is one of the materials that can accumulate in the protoplanetary disks around stars and thus develop into planets, moons and asteroids.
But astronomers did not expect this process to occur so early.
When the first stars (called population III stars) were born, in an era of the universe known as Cosmic Dawn, the only abundant elements around were hydrogen and helium. All the heavier elements did not yet exist. They could only form later, in the cores of stars, and would therefore not be observable until long after the death of the first stars.
Dying population III stars that explode as supernovae eject their heavier elements into the universe, allowing future stellar populations to develop rocky planets with more interesting chemistry.
The galaxy in question, called GS-z12, is believed to contain mostly second-generation stars built from the remnants of those first supernovae. Astronomers did not expect the building blocks of the Milky Way to be carbon-rich:
“We were surprised to see carbon so early in the universe, because the earliest stars were thought to produce much more oxygen than carbon,” says Maiolino. “We thought carbon was enriched much later, by entirely different processes, but the fact that it appears so early tells us that the very first stars may have functioned very differently.”
JWST’s Near Infrared Spectrograph allowed astronomers to split the light coming from the distant galaxy into its component parts, revealing all the different wavelengths present. Each element and chemical compound has its own signature when viewed via spectroscopy, and the signal for carbon was very strong. There was also a weaker signal for neon and oxygen, although these remain preliminary detections for now.
How carbon formed before oxygen is an open question, but one hypothesis suggests that scientists must now revise their models of Population III star supernovae. If these supernovae occurred with less energy than previously thought, they would scatter carbon from the outer shells of the stars, 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 at the beginning of the universe – much earlier than anyone could have imagined. JWST reveals unexpected details about the first galaxies that will ultimately make scientists’ predictions about the evolution of the universe much more robust. And perhaps most importantly, it also tells us about the very first step toward creating life.
“These observations tell us that carbon can be rapidly enriched in the early universe,” says Francesco D’Eugenio of the Kavli Institute. “And because carbon is fundamental to life as we know it, it is not necessarily true that life must have evolved much later in the universe. Life may have originated much earlier, but if there is life elsewhere in the universe, it could have evolved very differently than here on Earth.”
Learn more:
“The earliest detection of metal challenges what we know about the first galaxies.” University of Cambridge.
D’Eugenio et al. “JADES: Carbon enrichment 350 million years after the Big Bang in a gas-rich galaxy.” ArXiv preprint (accepted to Astronomy and astrophysics).