Using the James Webb Space Telescope (JWST), an international team of astronomers led by the University of Cambridge observed a very young galaxy in the early universe and found that it contained surprising amounts of carbon.
In astronomy, elements heavier than hydrogen or helium are classified as metals. The early universe was almost entirely made up of hydrogen, with small amounts of helium and tiny amounts of lithium.
Every other element that makes up the universe today was formed inside a star. When stars explode as supernovas, the elements they produce are distributed throughout their host galaxy, seeding the next generation of stars. With each new generation of stars and 'stardust', more metals are formed. Over billions of years, this process leads to a universe capable of supporting rocky planets like Earth and life as we know it.
Tracing the origin and evolution of metals will help scientists understand the transition from a universe made almost entirely of two chemical elements to the complex one observed today.
"The very first stars are the holy grail of chemical evolution," said lead author Dr. Francesco D'Eugenio from the Kavli Institute for Cosmology at Cambridge. "Since they are made only of primordial elements, they behave very differently to modern stars. By studying how and when the first metals formed inside stars, we can set a time frame for the earliest steps on the path that led to the formation of life."
Carbon plays a fundamental role in the evolution of the universe, as it can form grains of dust that clump together, eventually forming the first planetesimals and the earliest planets. Carbon is also crucial for the formation of life on Earth.
"Earlier research suggested that carbon started to form in large quantities relatively late - about one billion years after the Big Bang," said co-author Professor Roberto Maiolino, also from the Kavli Institute. "But we've found that carbon formed much earlier - it might even be the oldest metal of all."
The team used the JWST to observe a distant galaxy - one of the most distant galaxies yet observed - just 350 million years after the Big Bang, over 13 billion years ago. This galaxy is compact and low mass - about 100,000 times less massive than the Milky Way.
"It's just an embryo of a galaxy when we observe it, but it could evolve into something quite big, about the size of the Milky Way," said D'Eugenio. "But for such a young galaxy, it's fairly massive."
The researchers used Webb's Near Infrared Spectrograph (NIRSpec) to break down the light from the young galaxy into a spectrum of colors. Different elements leave distinct chemical fingerprints in the galaxy's spectrum, allowing the team to determine its chemical composition. Analysis of this spectrum showed a confident detection of carbon and tentative detections of oxygen and neon, though further observations will be needed to confirm these other elements.
"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."
According to some models, when the earliest stars exploded as supernovas, they may have released less energy than initially expected. In this case, carbon, which was in the stars' outer shell and less gravitationally bound than oxygen, could have escaped more easily and spread throughout the galaxy, while a large amount of oxygen fell back and collapsed into a black hole.
"These observations tell us that carbon can be enriched quickly in the early universe," said D'Eugenio. "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."
The results have been accepted for publication in the journal Astronomy and Astrophysics and are based on data obtained within the JWST Advanced Deep Extragalactic Survey (JADES).
The research was supported in part by the European Research Council, the Royal Society, and the Science and Technology Facilities Council (STFC), part of UK Research and Innovation (UKRI).
Research Report:JADES: Carbon enrichment 350 Myr after the Big Bang
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