Although they must have once existed, we haven’t yet spotted the first stars.
The very first stars to form in the Universe were different than the stars today: metal-free, extremely massive, and nearly all destined for a supernova surrounded by a cocoon of gas. There was a time, prior to the formation of stars where only clumps of matter, unable to cool and collapse, remained in large, diffuse clouds. It is possible that clouds that grow slowly enough may even persist until very late cosmic times.
Even at the observational frontiers, stellar populations aren’t pristine.
An illustration of the galaxy CR7, which was originally hoped would house multiple populations of stars of various ages (as illustrated). While we have yet to find an object where the brightest component was pristine, with no heavy elements, we fully expect them to exist, often alongside a later generation of stars that formed earlier. The merging of multiple star clusters is likely how the first galaxies and protogalaxies formed and took shape.
They all contain heavy elements, as well as a wide mix of stars.
This plot shows galaxies from the first ~1.5 billion years of cosmic history, color-coded by redshift and plotted by their metallicity (x-axis) as a function of the dust-to-stellar mass ratios (y-axis) found within them. The majority of low-metallicity galaxies are also dust-poor and are known as GELDAs, dominating the very early Universe, while later-time, more dust-rich galaxies are much more enriched in heavy elements. No pristine galaxies or stellar populations have yet been found, as of mid-2026.
There could be pristine, Population III stars among them, but that remains unproven.
This graph shows the combination of the Hubble, JWST NIRCam, and JWST NIRSpec data for galaxy RXJ2129-z8HeII. There is an unusually strong, blue tilt to the stellar spectrum of this object, but the evidence for any pristine material amidst the highly enriched gas and stars, with substantial fractions of heavy elements, that are present is too flimsy to make a compelling case for the presence of any pristine, Population III (a.k.a., the “first”) stars. No such population, as of mid-2026, has yet been found.
However, evidence of their one-time presence might persist in “relic” galaxies.
This chain of large galaxies is found near the center of the Perseus Cluster of galaxies, with several of these galaxies being typical of the large, bright, evolved galaxies found at the centers of most massive galaxy clusters. For many of these galaxies, the stars found inside of them are primarily older and redder, with only small populations of bluer stars found inside.
Some galaxies undergo intense star-formation briefly, and then never form stars again.
Galaxy clusters, like Abell S740, are the largest bound structures in the Universe. When spirals merge, for example, a large number of new stars form, but either post-merger or by speeding through the intra-cluster medium, gas can be stripped away, leading to the end of star formation in that galaxy and, eventually, a red-and-dead final structure. It is possible that red-and-dead galaxies can form much earlier in the Universe’s history than current observations indicate, with JWST offering hints that this is the case.
Because they expel or otherwise lose their gas, only their previously-formed stars persist.
Galaxies undergoing massive bursts of star formation expel large quantities of matter at great speeds. They also glow red, covering the whole galaxy, thanks to hydrogen emissions. This particular galaxy, M82, the Cigar Galaxy, is gravitationally interacting with its neighbor, M81, causing this burst of activity. Although the winds and ejecta are copious, this episode is not expected to completely “kill” this particular galaxy, as some gas will still persist after this episode completes.
Since brighter, bluer, higher-mass stars have the shortest lifetimes, they all die out.
When stars first form, the color-magnitude diagram (with brightness on the y-axis and color on the x-axis) looks like a curved line, from lower-right to upper-left. As the stars age, the brightest, bluest, most massive ones evolve off of this curve first. Identifying the point at which this “turn-off” occurs enables astronomers to determine the ages of the stellar populations within them, with only the youngest stellar populations containing the most massive stars. Many locations in the Universe have been identified where stars have not formed for 10 billion years or more: mostly globular clusters, but occasionally entire galaxies.
What remains are only the fainter, redder, lower-mass stars.
This is a blink comparison that plots the location of the red stars and blue stars that dominate the globular clusters in galaxies NGC 1277 and NGC 1278. It shows that NGC 1277 is dominated by ancient red globular clusters, but NGC 1278 contains many blue-colored ones. This is evidence that galaxy NGC 1277 stopped making new stars many billions of years ago, compared to NGC 1278, which has more young blue star clusters. The globular clusters located closer to the centers of these galaxies have preferentially higher metal contents, while the most distant ones have lower metal contents.
This creates “red-and-dead” galaxies, with the nearest major one being NGC 1277.
The ‘red-and-dead’ galaxy NGC 1277 is found inside the Perseus Cluster. While the other galaxies contain a mix of red-and-blue stars, this galaxy hasn’t formed new stars in approximately 10 billion years. Foreground, closer objects, like stars, as well as more distant galaxies, are all ubiquitous throughout this image.
Located within the Perseus Cluster, this cosmic time capsule resides 240 million light-years away.
This nearby galaxy, NGC 1277, although it may appear similar to other typical galaxies found in the Universe, is remarkable for being composed primarily of older stars. Both its intrinsic stellar population and its globular clusters are all very red in color, indicating that it hasn’t formed new stars in ~10 billion years. When all of the gas within a galaxy is expelled and no new gas enters, that galaxy becomes permanently “red-and-dead,” as no new populations of stars can form within it.
Astronomers recently imaged it with the EMIR instrument at the Gran Telescopio de Canarias.
Whereas most massive, late-type galaxies in the Universe exhibit a relatively standard abundance of silicon, red-and-dead galaxy NGC 1277, found just 240 million light-years away, has the strongest silicon signature ever observed in any galaxy. Because it has not formed stars in over 10 billion years, astronomers strongly suspect its silicon abundance is a signature left over from the first generation of stars.
Inside, they discovered a record-setting amount of silicon.
The high silicon abundance in NGC 1277, relative to the other elements and relative to other late-type galaxies, suggests enrichment from early populations of stars. According to Anna Ferré-Mateu: “NGC 1277 is unique because it formed most of its stars at a very early stage in the history of the Universe and then evolved almost passively. While other normal galaxies have erased their original chemical signatures by mixing with others, NGC 1277 has managed to preserve that excess of silicon intact, acting as the fossil record of the infancy of the Universe.”
Theoretically, the first stars produced enormous amounts of silicon.
The anatomy of a very massive star throughout its life, culminating in a Type II (core-collapse) supernova when the core runs out of nuclear fuel. The final stage of fusion is typically silicon-burning, producing iron and iron-like elements in the core for only a brief while before a supernova ensues. The most massive stars achieve a core-collapse supernova the fastest, typically resulting in the creation of black holes, while the less massive ones take longer, and create only neutron stars. The first stars, when they die in cataclysms, may produce a greater relative abundance of silicon than is generally found.
Credit: Nicolle Rager Fuller/NSF
The relative silicon abundance only decreases after future stellar generations live-and-die.
The relative abundances of elements in the Solar System has been measured overall, with hydrogen and helium being the most abundant elements, followed by oxygen, carbon, and numerous other elements. However, the compositions of the densest bodies, like the terrestrial planets, are skewed to be a vastly different subset of these elements. Overall, some ~90% of the atoms in the Universe, by number (but only ~70-72%, by mass), are still hydrogen, even after 13+ billion years of star-formation. Silicon remains an abundant element today, but was likely more abundant, relative to the other elements, after only one generation of stars had formed.
Credit: 28bytes/English Wikipedia
Lacking those later generations, NGC 1277 points to early, massive-star chemical enrichment.
Whereas most galaxies don’t just have an initial population of stars, but form stars throughout their history, leading to a mix of stellar populations and an averaged-out abundance of various elements, NGC 1277 may have formed just a few major bursts of stars early on, undergoing core-collapse and Type Ia supernovae afterward, to create its relic stellar population and enhanced silicon abundance today. It could provide a unique window into evidence for the first stars as a result.
Remnants from the first stars may provide the best explanation.
These six “little red dot” galaxies are examples of objects that, if their brightness was caused by the stars within them alone, could not have grown to such high masses in such short amounts of cosmic time under our currently prevailing cosmological picture. It’s possible that our cosmology is wrong, but it’s also possible, and perhaps more likely, that our naive assumption about the light from these objects being entirely due to stars is wrong. Learning about their silicon abundances could help determine the role that star-formation plays, and has played, within these objects.
Credit: NASA, ESA, CSA, STScI, Dale Kocevski (Colby College)
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