The most distant star, or possibly a pair of stars, that astronomers have ever seen has been revealed thanks to the Hubble Telescope and a massive cluster of galaxies. Far from Earth, the universe curves around the large mass of a galaxy cluster, creating a gravitational lens in space-time much like the curved lens of a magnifying glass. Like a magnifying glass, it revealed something small and hidden: a star system from the early universe.
The distant star system takes the official name WHL0137-LS, but the astronomers who found it nicknamed it “Earendel” from the Old English word for “morning star” or “rising light.”
The Eärendel system, as we see it today, shone just 900 million years after the Big Bang, according to the authors of a new article in the magazine Nature describing the discovery. It was 12.8 billion years before that light reached the Hubble Space Telescope, magnified by a trick of luck of gravity to appear as a tiny speck of photons on Hubble’s image sensor. Earendel is 8.2 billion years older than the Sun and Earth and 12.1 billion years older than the earliest animals on our planet.
Even by the standards of ancient stars, Eärendel stands out: Astronomers observed the previous record holder, nicknamed Icarus, as it appeared 9.4 billion years ago, 3.4 billion years more recently than this new record holder. Even the oldest known supernovae, usually the brightest and easiest to spot individual objects in the vastness of space-time, are younger than Eärendel.
See through the lens of gravity
Eärendel’s home galaxy, the Arc of Dawn, takes its name from the gravitational lensing effect that made this discovery possible.
“This galaxy appears enlarged and stretched into a long, thin crescent shape due to gravitational lensing from a massive foreground galaxy cluster,” said Brian Welch, an astronomer at Johns Hopkins University and lead author of the study. Nature paper.
Welch said the edge that he ran into Eärendel while studying gravitational lensing itself.
Gravitational lenses, like magnifying glasses, tend to warp and twist images and have areas of higher and lower magnification. If you have a magnifying glass at home, the best magnification is probably at the center of a simple circle. Gravitational lenses are more difficult to use.
In a gravitational lens, there is a line called the “critical curve” where the magnification is strongest. Objects seen through the lens are reflected off the critical curve and appear multiple times. And the more they line up with the line of the curve from our perspective on Earth, the more they get magnified.
“I was creating a model of galaxy cluster lensing, with the goal of measuring the broadening of the Arc of Dawn,” Welch said. “The models kept predicting that this bright spot in the arc should be at extremely high magnification.”
Welch realized that this bright spot was an object very closely aligned with the critical curve, so close and so small that even Hubble’s sharp eye resolved its reflected image duplicated across the line as a single speck. That proximity to the critical curve also meant that whatever it was, it had already been magnified between 1,000 and 40,000 times before reaching Hubble. As small and dim as it seemed to Hubble, it was, in fact, much smaller, tiny on the scale of the Sunrise Arc galaxy.
“As I investigated further, I discovered that the source was too small to be anything other than an individual star (or binary system),” Welch said.
the ancient universe
Welch and a large international team of co-authors spent three and a half years studying Earendel across multiple Hubble observations to confirm that they were seeing something real and not a transient effect of light.
That time and effort paid off, Welch said, because these very old stars can teach us about the history of the universe.
“With distant objects, we’re looking at the past of the universe and a time when the universe looked very different from today,” Welch said. “We know that galaxies look different at this early time, and we know that there have been relatively few generations of stars before.”
Stars are the heavy element factories of our universe, formed when lighter atoms like hydrogen and helium fuse together via nuclear fusion to form heavier materials like carbon, oxygen, and even iron. Earendel, at that early stage in our universe’s history, probably had very little material heavier than helium in its system, Welch said.
“Studying this lensed star in detail gives us a new window into what stars were like in these early days and how they differ from stars in the nearby universe,” Welch said.
The James Webb Space Telescope (JWST), launched in December 2021, is currently preparing for science operations. Its optics, sharper than Hubble’s, should be able to confirm their conclusion that Eärendel is a single star system and not a group of star systems clustered together, the authors wrote in the paper. They also hope to see if Eärendel was a lone star or a binary system, learn more about the star’s temperature and mass, among other properties.
JWST will be busy working its way through a science wish list that has grown long in the years astronomers have spent anticipating launch. What the edge previously reported. That will include studying exoplanets and the ancient universe, including star systems like Earandel that shone at the dawn of time.
Update 12:07 PM ET: This article has been updated with an additional image of Earandel and the Sunrise arc.