Scientists using two enormous telescopes — one on Earth and the other in space — have detected oxygen in the most ancient known galaxy, a star-scape beaming light just 300 million years after the Big Bang.
The galaxy, discovered with NASA's James Webb Space Telescope in 2024, is called JADES-GS-z14-0. In new observations involving the Atacama Large Millimeter/submillimeter Array in Chile, or ALMA, two separate groups of researchers not only measured its extraordinary distance with precision, but confirmed signals that oxygen was present.
The finding, along with other mounting evidence, has rocked the research community, challenging prior thinking that galaxies this long ago — when the universe was only two percent its age of 13.8 billion years — would not have had many elements heavier than hydrogen and helium. Before Webb, other telescopes like the Hubble Space Telescope and computer simulations suggested oxygen, carbon, and nitrogen didn't come about for perhaps another 200 to 400 million years.
The new studies, published in Astronomy & Astrophysics and The Astrophysical Journal, suggest the distant galaxy has about 10 times more heavy elements than expected, forcing scientists to rethink how early galaxies could have formed and evolved so quickly.
"Before the advent of JWST, we primarily observed 'nearby' galaxies, which provided a snapshot of an evolved universe," Stefano Carniani, a researcher at Scuola Normale Superiore in Italy and lead author of one of the studies, told Mashable. "Our understanding of the early universe was based on these observations, and we [had] assumed that this scenario remained unchanged across cosmic time."
The difference scientists are seeing between how galaxies mature now versus back then is that gas — the fuel of star formation — flows continuously and smoothly in contemporary galaxies, leading these stellar neighborhoods to grow steadily over long periods of time, Carniani said. But observations of ancient galaxies like JADES-GS-z14-0 suggest that gas flows were far more chaotic. These galaxies sometimes appear to have accumulated vast reservoirs of gas.
"Even if only a small fraction was converted into stars, their rapid growth and evolution were inevitable," Carniani said.
The leading theory used to be that the first stars — the confusingly named "Population III stars" — were formed in the early universe, mostly before elements heavier than helium existed. Those original stars are thought to have been extremely massive, luminous, and hot. Eventually, they would have died in violent supernovas, blasting out new types of chemical substances.
Heavier elements are forged in the cores of stars, only to be scattered across interstellar space after the stars explode. Those outbursts would seed the universe with the first heavier elements, but astronomers thought it would take several generations of stars before galaxies were brimming with enough oxygen and other such elements to be detectable.
But another thing to consider is that very massive stars don't live long — at most, a few million years, Sander Schouws, a researcher at Leiden Observatory in the Netherlands and lead author on another of the papers, told Mashable. That might explain how heavier elements could have flooded the galaxy rather quickly back then.
So far Webb has revealed that, in fact, many bright galaxies existed at cosmic dawn, a period between 100 million years to 1 billion years after the Big Bang. Some scientists have posited that perhaps galaxies in this era formed stars more efficiently, leaving behind little extra gas and dust. If there were too much gas, it would essentially dilute those heavier elements, making them hard to detect.
Others suggest that powerful starlight forced gas and dust out, making the galaxies seem brighter because less material was available to obscure them. Still, some theories propose that supermassive black holes powering enormous jets could explain the galaxies' brightness, though the studies of JADES-GS-z14-0 have not found evidence of one.
Images of the ancient galaxy have shown its brightness to be spread out across 1,600 light-years, indicating that most of its light comes from young stars and not a concentration of black hole emissions at its center. If the estimates are correct, the galaxy is several hundreds of millions of times the mass of the sun.
Schouws points out another factor that could complicate astronomers' interpretation of what's going on in this old galaxy: A phenomenon called bursty star formation could make it appear as if it's forming a lot faster than it really is.
In bursty star formation, galaxies become intermittently bright. That could make it seem in a single snapshot as if the galaxy is growing a lot faster than if scientists were to average that brightness over a longer period of time. Rather than making stars at a steady clip like the Milky Way does, for instance, these galaxies churn out stars inconsistently, with a proliferation all at once, followed by stagnant periods sometimes stretching millions of years.
The thinking is that a burst of stars, all of the same generation, form and then die off in supernovas a few million years later at about the same time. The gas may then be recycled to form new stars, but the process is irregular at best.
"This is an effect that we need to account for," Schouws said, "but that can be tricky."
Topics NASA
