JWST could finally spot the very first stars in the universe
NEWS | 25 January 2026
Earendel, the current record holder for most distant star ever seen, is circled in this image from NASA's James Webb Space Telescope. The star is contained within the Sunrise Arc, a magnified and distorted galaxy from the early universe. On Christmas Day 2021, alongside other astronomers, I watched the James Webb Space Telescope (JWST) launch from French Guiana and begin its month-long journey to its destination, 1.5 million kilometers from Earth. The trip was filled with many nerve-racking moments, particularly the week-long period in which the telescope’s tennis-court-size sun shield array slowly unfolded like origami from its bus-size liftoff configuration. Luckily, JWST made the trip safely and began operations in the summer of 2022. Since then, the observatory has started answering some of the biggest questions in astronomy. It’s also raised many new ones. One of the biggest surprises that has emerged is the discovery that supermassive black holes, some with masses more than a million times that of the sun, existed when the universe was no more than about 3 percent of its current age. How such massive black holes came to exist so long ago is a puzzle. Perhaps less massive black holes formed from the explosive deaths of the first stars, known as Population III stars, and those black holes later merged under the influence of gravity to form a million-solar-mass black hole. On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. But how could thousands of these smaller black holes have combined in the cosmically short period of hundreds of millions of years? To figure it out, we need to understand the very first stars, which, to date, no one has ever seen individually. Known as dinosaur stars for both their primeval nature and their immense size, Population III stars existed only when the universe was very young. At that time chemistry was simple. The stars would have been made of hydrogen, helium and tiny traces of light elements such as lithium because those were the only elements that existed then. It’s simply amazing that humans can hope to observe such relics from the very beginning of time. In such a pristine environment, when the universe was much denser than it is today, much more massive stars were able to form than those we can observe now. Such large stars are the analogues of 20th-century rock stars—or pop stars (pun intended). They lived fast and died young, and like all great rock bands do, they left a mark on the universe. During their short lives, just a few million years long, Population III stars churned out heavier elements such as carbon, oxygen, nitrogen, silicon, sulfur and iron through fusion within their cores. When they died in supernova explosions, those elements poured into the universe and seeded the ingredients that would later be essential to form planets and life as we know it. What was left after one of these supernovae was, in most cases, a black hole. Scientists have yet to observe Population III stars individually, but that could soon change. Thanks to JWST, along with a helpful boost from nature called gravitational lensing, we might get a glimpse of them as they were during their brief lifetimes or be able to detect their very bright final explosions. We might even see the shining gas around their skeletal black holes, which would appear to us as a small quasar. It’s simply amazing that humans can hope to observe such relics from the very beginning of time. These stars won’t just teach us about the early universe—they might also shed light on one of its biggest mysteries: dark matter. The cosmos seems to be filled with invisible matter we don’t understand, but the light of the first stars must have traveled through it on the way to our telescopes, so this light can teach us about its nature. My personal journey to study these early stars started more than 10 years ago, after I had worked on different astronomical questions at several institutes across the U.K., the U.S. and Spain. At that point I temporarily relocated to the U.S. to work with data from the best telescope at the time, NASA’s Hubble Space Telescope, and on my favorite topic, gravitational lensing. The primordial galaxy known as the Sunburst Act appears four times in this image from the Hubble Space Telescope. The light from the galaxy, which lies 11 billion light-years away, has been distorted and magnified into curving smudges by the mass of the galaxy cluster in the center of the image. One of the oldest known stars, Godzilla (circled), is visible within this galaxy. ESA/Hubble, NASA, Rivera-Thorsen et al., CC BY 4.0 As powerful as the Hubble and James Webb telescopes are, they are not large enough to see Population III stars without a boost. Fortunately, the universe has been kind to astronomers and has built thousands of naturally occurring telescopes that magnify the distant galaxies lying behind them. Similar to the way a piece of glass can be turned into a magnifying lens that curves light, very massive objects in the universe can bend space itself. When light travels through this warped space, it also bends. Albert Einstein predicted this molding of space and light, which is known as gravitational lensing. The most massive objects in the universe, and thus the most powerful natural lenses, are galaxy clusters, swarms of hundreds to thousands of galaxies packed together in a relatively small volume that also contains vast amounts of the mysterious substance called dark matter. Galaxy clusters can have masses up to 1,000 times that of the Milky Way and are held together by gravity. When we point a telescope at one of them, the cluster’s gravity both amplifies and distorts our view of the background galaxies, thereby creating the gravitational lens. Light from an object behind the center of the lens will be amplified and distorted into a circular shape called an Einstein ring. Matthew Twombly When we point JWST toward a gravitational lens, we are adding an extra giant lens in front of the telescope, effectively transforming the observatory into a cosmic microscope. Gravitational lenses magnify only a small portion of the space behind them, just as microscopes do. And the magnification provided by the gravitational lens is not uniform: most of the area behind the galaxy cluster is magnified by factors of less than 10, but in some very small regions, termed caustics, the effect can be very strong, with magnification factors of up to around 10,000. If a sufficiently bright but small object happens to be in one of these caustics, we can get an otherwise impossibly zoomed-in view of it. When JWST points at one of them, it acts like a telescope 100 times larger than it is, offering the opportunity to take a very high-resolution peek at the distant universe. The only catch is that the objects we can observe with this technique must be relatively small and bright. Population III stars meet these two requirements. Astronomers are getting close to scoring front-row seats to these elusive stars. In recent years we have glimpsed some of the most ancient stars yet. In 2016, five years before the launch of JWST, astronomers used the Hubble telescope to spot Icarus, the first star observed through a cosmic microscope. Icarus lies a whopping 200 times farther away than the most distant star known before it. Patrick Kelly of the University of Minnesota, who led the team that discovered Icarus, named it after the mythological character who flew too close to the sun, in reference to the high magnification that revealed it. The scientists first noticed Icarus because its brightness fluctuated between observations separated by months. Very few objects in the universe exhibit this type of change in brightness; after considering all plausible options, the researchers determined that a blue supergiant star was the only possible candidate that could explain the observations. The brightness fluctuations were the result of a different lensing effect, microlensing, produced by much smaller masses. For most astrophysical objects, this effect is negligible. But for background stars whose magnification can change considerably in a matter of weeks, such as Icarus, it can lead to dimming and brightening. When a microlens temporarily aligns with a telescope, a galaxy cluster lens and a distant background star, the star’s brightness can increase by up to a factor of 10. The alignment tends to last for a few weeks. During microlensing episodes, the background star twinkles in a well-known and predictable way that allows us to recognize it as an individual star. Lensed stars can help us map the distribution of dark matter and reveal some of its properties. Microlensing is produced mostly by stars in a galaxy cluster, but it can also arise from small concentrations of mass, including structures composed of dark matter. Microlensing can act as an additional lens in the cosmic microscope, increasing its power even further. Icarus held the record as the most distant star ever observed for a few years, until the 2022 discovery of Earendel. This star—discovered by a team led by Brian Welch, then at Johns Hopkins University, and Dan Coe of the Space Telescope Science Institute—was found to be five times farther away. Of course, Icarus and Earendel are long gone; we are seeing them as they were billions of years ago because their light has taken that long to reach us. Earendel, for instance, appears as it existed when the universe was 7 percent of its current age. The estimated gravitational lensing magnification for Earendel is close to 10,000 times—the highest magnification observed so far. Earendel is the closest we have come to observing Population III stars, and astronomers think some of these original stars were still around at the time our observations of Earendel represent—so we may soon see them, too. Most likely, however, we will need to observe further back in time to see the first generation of stars. Recent years have witnessed the discovery of tens of individual stars at extreme cosmic distances. On its journey to us, their light has crossed half the universe and gathered valuable information along the way. This light can tell us, for instance, about dark matter, a substance of unknown composition that permeates the entire cosmos. By far the most abundant form of matter in the universe, dark matter has evaded detection by the most advanced laboratories on Earth. It might be made of particles a tiny fraction of the size of an electron, or it might consist of black holes harboring masses comparable to the sun’s. Regardless of what it is, dark matter virtually ignores ordinary matter (and our expensive detectors). Fortunately for us, lensed stars can help us map the distribution of dark matter and reveal some of its properties. If dark matter in the gravitational lens forms invisible structures with masses comparable to or larger than those of planets, these structures will introduce a small but measurable change in the magnification of the lensed star. My team and I, now based at the Institute of Physics of Cantabria in Spain, have measured this type of anomaly in at least two lensed stars, named Godzilla and Mothra. This research revealed two invisible structures with masses in the range of tens of thousands to hundreds of millions of solar masses. If these structures are dominated by dark matter, they will rule out certain theories of dark matter under which it couldn’t form such small structures. Future observations of these and other lensed stars can tell us more about what dark matter can and can’t be. An early star named Mothra (circled) appears in an ancient galaxy that existed three billion years after the big bang. The light from the galaxy and its stars has been warped and magnified by the mass of the galaxy cluster MACS0416, as seen in this image made with combined data from the Hubble and James Webb Space Telescopes. NASA, ESA, CSA, STScI, Jose Diego (IFCA), Jordan D'Silva (UWA), Anton Koekemoer (STScI), Jake Summers (ASU), Rogier Windhorst (ASU), Haojing Yan (University of Missouri); Image Processing: Joseph DePasquale (STScI) Perhaps the most spectacular lensed stars we have discovered lie in the Dragon Arc galaxy, the first lensed galaxy ever observed, which was seen in the second half of the 20th century. The Dragon Arc isn’t extremely far from us—it’s “only” 6.5 billion light-years away. But many areas within the galaxy are magnified by factors exceeding 100, so we see the galaxy as it would look to a telescope 10 times larger than JWST. James Webb observed the Dragon Arc in 2023 and discovered more than 40 individual stars through their twinkles. Some studies of the stars in the galaxy suggest that dark matter may be composed of incredibly small particles, even lighter than the hypothetical axion predicted by quantum chromodynamics, a popular dark matter candidate. These studies also suggest that dark matter may have bizarre quantum properties that scientists call “fuzzy,” giving dark matter weird wavelike characteristics. At press time, JWST was poised to observe the Dragon Arc once more in search of new lensed stars to help answer these questions. Using the latest telescopes along with nature’s lenses to observe ancient stars puts us in a new golden era of astronomy. JWST is regularly discovering distant stars, and new observatories are set to join it. NASA’s Nancy Grace Roman Space Telescope, to be launched in late 2026, will observe about 12 percent of the sky and should reveal thousands of new lensed galaxies at vast distances. Astronomers will then use JWST to observe the most promising candidates for harboring Population III stars in the hope that we can catch a primordial star near the region of high magnification. Other space telescopes, such as the European Space Agency’s relatively new Euclid observatory, are monitoring even larger areas (about 30 percent of the sky) and are already uncovering myriad new gravitational lenses. Some of these lenses could be the first to reveal Population III stars when reobserved with JWST. Even more exciting is the potential of a future NASA mission, the Habitable Worlds Observatory (HWO), which will have capabilities surpassing those of JWST in some ways. This supertelescope is still under consideration by NASA, and its final design and specifications have yet to be defined. Already, though, it promises an unparalleled opportunity to see the most distant stars. Many Population III stars, for instance, are thought to be very hot and might be too warm to be detected by JWST, which is better suited for cooler stars. Our knowledge of the best natural gravitational lenses and the best magnified galaxies to observe will have advanced significantly by the time this new telescope is launched. Perhaps by then the first dinosaur stars will have already been confirmed, and we can study them in greater detail with HWO. These tools should help us extend our frontier even further back in time, closer to the beginning of the cosmos, revealing the universe’s first stars as well as our own origins.
Author: Clara Moskowitz. José María Diego Rodríguez.
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