Astronomers spot the most distant single star ever seen using a cosmic telescope predicted by Einstein

Close-up of the region of sky, 1/250 of a degree in diameter, where the gravity of a cluster of galaxies in the foreground magnifies the distant background star – nicknamed Earendil – thousands of times. Credit: Science: NASA, ESA, Brian Welch (JHU), Dan Coe (STScI), Image processing: NASA, ESA, Alyssa Pagan (STScI)

Hubble spots the most distant single star ever seen, at a record distance of 28 billion light-years.

With a fortuitous range of a massive cluster of galaxies, astronomers among other institutes at the University of Copenhagen and DTU have discovered a single star in most of the observable Universe. This is the most distant detection of a single star ever. The star can be up to 500 times more massive than the Sun.

Looking at the night sky, all the stars you see are in our own galaxy, the Milky Way. Even with the most powerful telescopes, under normal circumstances, individual stars can only be resolved in our nearest galactic neighbors. In general, distant galaxies are thought of as the mixed light of billions of stars.

But with the wondrous natural phenomenon known as “gravitational lensing,” astronomers at the Niels Bohr Institute’s Cosmic Dawn Center and DTU Space have nonetheless been able to detect a distance where even detecting entire galaxies is difficult.

A cosmic telescope predicted by Einstein

Among the wonders predicted by Einstein’s theory of relativity is the ability of mass to “bend” space itself. When light passes close to massive objects, its trajectory follows the curved space and changes direction. If a massive object is between us and a distant background light source, the object can deflect and focus the light towards us like a lens, magnifying the intensity.

Massive galaxy cluster focuses and amplifies light for Hubble

A massive galaxy cluster focuses and amplifies light from a background galaxy. Credit: Peter Laursen

Galaxies magnified several times are regularly discovered by this method. But in a stunning cosmic coincidence, the galaxies in a cluster named WHL0137-08 aligned in such a way as to focus the light from a single star towards us, magnifying its light thousands of times.

A combination of this gravitational lens and nine hours of exposure time with the The Hubble Space Telescope enabled an international team of astronomers to detect the star.

Earendel – the morning star

Astronomers nicknamed the star Eendel, from Old English meaning “morning star” or “rising light”. They calculate that the star is at least 50 times more massive than our Sun, possibly as much as 500, and millions of times brighter.

Besides being an amazing achievement in itself, the Earendel observation offers a unique opportunity to investigate the early Universe:

“Looking out into the cosmos, we are also looking back in time, so these very high-resolution observations allow us to understand the building blocks of some of the earliest galaxies“, explains Victoria Strait, post-doctoral researcher at the Cosmic Dawn Center in Copenhagen, and collaborator and co-author of the study. She specifies:

“When the light we see from Earendel was emitted, the Universe was less than a billion years old; only 6% of his current age. At that time, it was 4 billion light-years from the proto-Milky Way, but during the almost 13 billion years it took light to reach us, the Universe expanded. so that it is now 28 billion light years away.

The previous record is a star seen when the Universe was about a third of its current age, by which time most of its structure had already formed and evolved. So Earendel is indeed a revolutionary record.

Mirrored Star Cluster Earring

Close-up of the tiny region where Earendel fell just above the narrow line where the magnification increases by (tens of) thousands of times. A cluster of many stars is seen slightly offset from the line, which results in much lower magnification but is instead reflected by gravity. Credit: NASA/ESA/Brian Welch (JHU)/Dan Coe (STScI)/Peter Laursen (DAWN)

A target for the James Webb Space Telescope

To measure Earendel’s luminosity, astronomers built a physical model of the gravitational lens. The exact nature of the light source depends on their model, but when astronomers are so certain that the tiny dot is actually a single star, it’s partly because many different models all give roughly the same answer.

Nevertheless, Earendel could in principle be more than one star, located very close to each other. To test if this is the case, the team requested – and was granted – observation time with the recent launch James Webb Space Telescope.

Massive galaxy cluster concentrates and amplifies light for Webb

A massive galaxy cluster focuses and amplifies light from a background galaxy. Credit: L. Hustak, STScI

“With James Webb, we will be able to confirm that Earendel is indeed just a star, and at the same time quantify what type of star it is,” says Sune Toft, head of the Cosmic Dawn Center and professor at the Niels Bohr Institute. , who also participated in the study. “Webb will even allow us to measure its chemical composition. Potentially, Earendel could be the first known example of the first generation of stars in the Universe.

To learn more about this discovery, read Hubble spots the most distant star ever seen thanks to lucky cosmic alignment.

Reference: “A star highly magnified at redshift 6.2” by Brian Welch, Dan Coe, Jose M. Diego, Adi Zitrin, Erik Zackrisson, Paola Dimauro, Yolanda Jiménez-Teja, Patrick Kelly, Guillaume Mahler, Masamune Oguri, FX Timmes, Rogier Windhorst, Michael Florian, SE de Mink, Roberto J. Avila, Jay Anderson, Larry Bradley, Keren Sharon, Anton Vikaeus, Stephan McCandliss, Maruša Bradac, Jane Rigby, Brenda Frye, Sune Toft, Victoria Strait, Michele Trenti, Soniya Sharma, Felipe Andrade-Santos and Tom Broadhurst, March 30, 2022, Nature.
DOI: 10.1038/s41586-022-04449-y

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