The James Webb Space Telescope (JWST) was built primarily to transform our understanding of the early universe. Less than a year after it was switched on, it is delivering, finding galaxies earlier in the universe than any seen before. Yet the telescope has another, less publicized goal in probing those earliest moments after the big bang 13.8 billion years ago. It is hunting for signs of the first stars to switch on in the universe, so-called Population III stars, gigantic balls purely made of hydrogen and helium that shined brilliant and brightly to first bring light to the cosmos. “They’ve been sort of in the background,” says Garth Illingworth of the University of California, Santa Cruz, largely because finding them is so difficult. No definitive detection of such stars has ever been made, but we know they must exist. Now two new results are bringing us closer than ever before to their discovery.

In a pair of papers posted on the preprint server, two teams of astronomers report promising signs of Population III stars. In the first study, led by Roberto Maiolino of the University of Cambridge, researchers think they may have found a pocket of Population III stars nestling in the outskirts of a remote galaxy. The second study, led by Eros Vanzella of the National Institute for Astrophysics in Italy, hints at a tiny galaxy that may be composed of, if not Population III stars per se, extremely primordial stars born early in the cosmos. “These papers quite nicely highlight the different aspects of the search,” says Jorryt Matthee of the Swiss Federal Institute of Technology in Zurich, who was not involved with either paper. “We’re almost there.”

Once the universe had cooled and calmed sufficiently about 400,000 years after the big bang, the first atoms were able to form: hydrogen and helium. These atoms would have clumped together into immense clouds under gravity and eventually formed Population III stars. Unhindered by competition from other stars, these stars may have grown to huge sizes within these clumps—at least hundreds or even thousands of times more massive than our sun. This bulk meant the stars were short-lived, exhausting their fuel and exploding as supernovae within just a few million years. Yet those explosions were vital to the universe. They released heavier elements that had formed inside the stars, such as oxygen and carbon, which gave rise to Population II stars and, later, Population I stars such as our sun and even planets such as Earth and life itself.

Those short lifetimes have made tracking down Population III stars difficult but not impossible. Some clouds of primordial gas should have persisted for some time after the big bang, perhaps hundreds of millions of years. Meanwhile the immense heat of the stars, about 90,000 degrees Fahrenheit on their surface—10 times that the temperature of our sun—should give off a telltale hint of helium that could only have been produced at such temperatures. Because they are very small from our viewpoint and likely muddled with later Population II stars, however, they have been undetectable by most telescopes—until JWST. From the early planning of the telescope in the 1980s, the focus had been on galaxies. “When it came to the scientific discussions about the potential of JWST, it was always about the earliest galaxies,” says Illingworth, who is former deputy director of the Space Telescope Science Institute, which runs JWST. “For political purposes, we tried to keep it very simple.” Yet the possibility of finding Population III stars has always been a tantalizing, if extremely difficult, possibility. “Searching for Population III stars in the early universe is a key part of the science that JWST was built to accomplish,” says Jane Rigby of NASA’s Goddard Space Flight Center, who is operations project scientist for JWST.

Doing so would be “a huge discovery,” says Rebecca Bowler of the University of Manchester in England. “We still haven’t seen the smoking gun of Population III stars. They are a missing piece in our understanding of the history of the universe.” One galaxy touted as a potential host of Population III stars prior to JWST, called CR7, was seemingly ruled out in 2017. A more recent result from JWST earlier this year found tentative hints in a distant galaxy, but the results remain inconclusive. “We haven’t had an instrument that could find them before,” Bowler says. “JWST is our best shot—it’s huge, and it’s got the right wavelength coverage.”

Maiolino’s team used JWST to observe a galaxy called GN-z11 that was previously discovered by the Hubble Space Telescope in 2015. GN-z11 dates back to just 400 million years after the big bang and was the most distant known galaxy until JWST discovered ones that are farther away. Picking apart the light at the galaxy’s edge in a process called spectroscopy, they found hints of helium that could be linked to small pockets of Population III stars in the galaxy’s outer regions. If correct, the stars in the clump would have masses at least 500 times that of our sun, with a total mass of 600,000 solar masses, which would explain the signal seen by the team. “We are pushing the telescope to its limits,” Maiolino says. “These could be clumps of gas that didn’t fully mix with the rest of the galaxy.” Another possibility is that the signal came from a direct collapse black hole, an example of theorized, never-before-seen objects tens of thousands of times the mass of our sun that were the seeds of supermassive black holes. That would “still also be an extremely exciting discovery,” he says.

Vanzella’s team takes a different approach. Using the gravitational bulk of a galaxy cluster called MACS J0416, the team detected what appears to be a magnified emission of hydrogen and a small amount of oxygen from a very small and very remote galaxy. “It’s magnified by a factor of maybe 500,” says Mark Dickinson of the National Science Foundation’s National Optical-Infrared Astronomy Research Laboratory (NOIRLab) in Arizona, who is a co-author of the paper. While the researchers were not able to see the light of the galaxy directly, their findings suggest the presence of two extremely small clumps of stars in the early universe, perhaps totaling less than 10,000 solar masses altogether and seen about 800 million years after the big bang. The clumps do not seem to be solely composed of Population III stars, but the amount of heavy elements present is incredibly small. “The heavy element abundance is lower than anything else we have seen in the universe,” Dickinson says. “It’s as close to a primordial galaxy as we’ve seen.”

While neither paper is a definitive detection of Population III stars, both are among our best evidence yet for their existence. “They’re closer, but they’re not conclusive,” says Daniel Whalen of the University of Portsmouth in England, who was not involved with the research. Bowler says that while neither paper “ticks all the boxes,” both “are very interesting and point in the direction of Population III.” Further studies of both targets would be needed to truly ascertain whether they contain primordial or at least close to primordial stars.

Another result published last week in Nature finds a hint of Population III stars closer to home. Astronomers studied a star in the halo of our galaxy and found that it contained an unusual composition of heavy elements and had a sodium deficiency. This suggests it may have formed from the ashes of a Population III star in a theorized pair-instability supernova, which occurs when a star between 140 and 260 times the mass of our sun experiences a runaway thermonuclear explosion. “We know first generation stars can produce such chemical element patterns,” says Gang Zhao of the Chinese Academy of Sciences, who is one of the paper’s co-authors. The team estimates the second-generation star they observed is more than 13 billion years old, forming just 500 million years after the big bang following the death of a Population III star.

Upcoming work, particularly by researchers using JWST, will bring us closer to seeing light directly from Population III stars. Hannah Übler of the University of Cambridge and Maiolino successfully proposed to use JWST in its second year of science, starting in July, to observe seven galaxies in the early universe that appear to have low amounts of heavy elements. “We want to look in the surroundings of these galaxies to see whether we can find Population III stars in their outskirts,” Übler says. “We would then be able to constrain, with some assumptions, the mass of the stars.” Another JWST program, led by Matthee, will search for gas clouds “in or around galaxies” in the early universe that lack heavy elements, Matthee says.

Seeing such clumps of Population III stars may be the limit of what is possible with JWST, allowing us to confirm the existence of these stars at particular epochs of the universe and telling us something about the sizes they grew to. There is a slim possibility, however, that the telescope may be able to resolve individual Population III stars if they are magnified sufficiently, perhaps around a galaxy cluster, in future observations. “In principle, it’s possible, but you would have to be extremely lucky,” Übler says, adding that it will require magnifications of 1,000 times or more. For now, our best bet is looking for the emission from small clumps of stars, a task JWST is perfectly suited to. If we can find them, it opens a whole new understanding of how our universe began. “We want to know how everything started,” Maiolino says. “Without the chemical enrichment of first-generation stars, there wouldn’t have been anything else. It’s a key epoch in the formation of our universe.”