About 12.9 billion years ago, at the dawn of the known universe, a star was born. It was 50 times bigger than our Sun and a million times brighter, and—like much of the early universe—was probably composed of mainly lighter elements, like hydrogen and helium.This star burned fast and bright, and likely only lived for a million years—the blink of an eye in cosmic timescales. Now nicknamed Earendel after the old English for “morning star,” it would have remained unknown if not for a series of remarkable coincidences that allowed it to be spotted by the Hubble space telescope and become the most distant star ever seen from Earth.
Earendel’s discovery offers a glimpse into the first billion years after the Big Bang, when the universe was just 7 percent of its current age. At 12.9 billion light-years away, it smashes the previous record of 9 billion, which was also set by Hubble when it observed a giant blue star called Icarus in 2018.
Until now, the smallest objects seen at this distance have been clusters of stars inside early galaxies. “It’s quite crazy that we can see a star that far away,” says Guillaume Mahler, from the Center of Extragalactic Astronomy at Durham University in the United Kingdom, who was part of an international team that worked on the research. “No one would have hoped that we would have been able to see it.”
In fact, Earendel might be the farthest star we are ever able to see because spotting it was only possible thanks to what NASA astronomer Michelle Thaler calls “a coincidence of stellar proportions.” The star happened to be perfectly lined up with both Hubble and a kind of natural zoom lens offered by a huge galaxy cluster that sits between Earth and Earendel. Through a phenomenon known as gravitational lensing, this cluster, called WHL0137-08, acted as a magnifying glass, warping the fabric of space and amplifying the light of distant objects behind it. “This cluster of galaxies is actually producing this wonderful lens, kind of a natural telescope—a telescope made of space itself,” Thaler says.
That amplified Earendel’s light by a factor of thousands and allowed Hubble to see farther than ever before. “It’s an incredible distance. And what’s special about it is, because the light has taken 12.9 billion years to reach us, we’re seeing the universe practically as a baby,” says Becky Smethurst, an astrophysicist at the University of Oxford who was not involved in the research. She and others liken the phenomenon of gravitational lensing to the bright patterns of light at the bottom of a swimming pool, which are created by ripples of water on the surface catching and concentrating the sunlight.
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“We almost didn’t believe it at first, it was so much farther than the previous most distant star,” Brian Welch, a PhD student at Johns Hopkins University and lead author of a Nature paper detailing the discovery, stated in a NASA press release. “Normally at these distances, entire galaxies look like small smudges. The galaxy hosting this star has been magnified and distorted by gravitational lensing into a long crescent that we named the ‘Sunrise Arc.’”
By studying this arc in detail, as part of Hubble’s RELICS (Reionization Lensing Cluster Survey) program—which analyzes images taken through these gravitational lenses to peer into the early universe—Welch was able to spot Earendel, which “popped” out from the general glow of its home galaxy, thanks to the lensing effect that amplified its brightness. Welch is a fan of the works of J.R.R. Tolkein and named the star after a character from The Silmarillion whose name means morning star. “We thought that was very apropos, because this is a star from the dawn of stellar formation, the dawn of time,” says Thaler.
Although Earendel is long dead, looking at its “baby pictures” can give us important clues about the nature of the universe and the origins of matter. “You’re actually looking at the time when most of the chemical elements that make up our bodies were formed,” Thaler says. “The universe began with just hydrogen and helium gas. That’s it. Everything else, like the calcium in my teeth or the iron in my blood, had to be formed inside stellar cores that then blew up. And so this first generation of stars produced a huge amount of these heavier, richer chemicals, the things that make life possible.”
Researchers have been able to make basic inferences about Earendel based on its luminosity and color profile. But to find out more—and confirm that it is indeed a single star rather than a binary or triple star system—more observations will be needed. That’s where the newly launched James Webb Space Telescope could play an important role. Hubble is 32 years old and has maybe a decade of life left, so the fact that the star has lined up with the gravitational lens during the brief window when both Hubble and the JWST are available to image it is another stroke of good fortune for scientists. “The two working together will reveal so much more about the universe than we’ve ever known before,” says Smethurst.
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Unlike Hubble, which sees mostly in the visible light spectrum, the JWST sees in infrared, which will give it more information about the chemical composition of Earendel. “Webb can actually hone in on that, do some spectroscopy, separate the light into a rainbow to figure out what the chemistry is, what the temperature of the star is, all of that,” says Thaler.
There’s a small chance that Earendel could be what’s known as a Population III star—a hypothetical category of stellar objects comprised purely of hydrogen and helium, which were around immediately after the Big Bang. “We haven’t got any of them like that in the Milky Way because it’s a lot older,” says Smethurst. “It could prove this one last piece of this theory of nucleosynthesis—how elements come to be formed in stars.”
Even if it doesn’t turn out to be a Population III star, studying Earendal and other distant stellar objects could tell us more about when certain elements first materialized. “If it reveals it does have some lithium or beryllium, for example, it’ll tell us when those elements started to get formed,” says Smethurst. “If it is all hydrogen, it’ll tell us how fast the heavier elements formed in the early universe, or at what point you start getting planets and the early conditions for life. Was it a billion years after the Big Bang, or 2 billion years? Could an intelligent civilization have come and gone in that time?”
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