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Hubble telescope detects most distant star ever seen, near cosmic dawn

A long time ago in a galaxy far, far away, there was a large and magnificently brilliant star that shined across the young, expanding universe. The starlight skewed blue. It was the cosmic morning, when everything in the universe was still new, raw, the galaxies still forming not long after the first stars had ignited and lit up the heavens.

The light from that blue star traveled through space for billions of years, and then one day a few thin beams crashed into a polished mirror — the light bucket of the Hubble Space Telescope.

In a report published Wednesday in the journal Nature, a team of astronomers asserts that this is the most distant individual star ever seen. They describe it as 50 to 100 times more massive than our sun, and roughly 1 million times brighter, with its starlight having traveled 12.9 billion years to reach the telescope.

The lead author on the report, Brian Welch, a 27-year-old doctoral candidate at Johns Hopkins University, had the honor of giving the star a name: Earendel. It’s an Old English word, meaning “morning star,” he said. Earendel was found in a young galaxy known as the Sunrise Arc, and “morning star” seemed appropriate, Welch said.

“And it sounds cool,” he added. Moreover, “Earendil” is the name of a character in J.R.R. Tolkien’s “The Silmarillion,” which also inspired the name, Welch said.

“This is one of the major discoveries of the Hubble Space Telescope in its 32 years of observation,” said Rogier Windhorst, an Arizona State University astronomer and a co-author of the report.

Found in the constellation Cetus near the star Mira, Earendel’s light was emitted about 900 million years after the universe began its expansion — the big bang. If that estimated distance holds up to further scrutiny, the starlight would have been emitted nearly 4 billion years further back in the universe’s history than that of the most distant individual star previously seen.

In recent decades, astronomers have seen galaxies at that distance, and even farther away, but galaxies are collections of billions of stars and the very distant ones have typically been nothing more than smudges of light.

As with any stunning claim, this carries caveats and uncertainties, starting with the possibility that it is not a singular star at all. It’s possible Earendel is a pair of stars, or even a trio or more, a common stellar phenomenon in which one bright member of the group does most of the illumination. (Alpha Centauri, the closest sun-like star, is part of a triplet).

Another possibility is that Earendel is, at its core, a black hole — the remnant of a massive individual star that has collapsed. Black holes are invisible, of course, but their gravity can lure rapidly moving and visible material, known as an accretion disk.

“The object is real. It’s not a smudge. There is something there,” Windhorst said. “The question is, whatever object is there, what is it really?”

What it definitely is, is a target for the newly launched James Webb Space Telescope, the Hubble’s successor. The Webb is parked in a solar orbit that keeps it roughly 1 million miles from Earth, and it is in the midst of a calibration and commissioning phase, with the first scientific observations still a few months away.

The discoverers of Earendel have snagged observation time on the Webb. The new space telescope has the ability to study, in a way that Hubble can’t, the elemental composition of Earendel.

The previous record holder for the most distant individual star is named Icarus, detected by the Hubble in 2018 and seen in a galaxy whose light was emitted 9 billion years ago, when the universe was about one-third its current age, according to NASA.

Earendel emitted its light remarkably close to the cosmic dawn — the epoch when the first stars ignited and galaxies began to form. The current estimate for the age of the universe is about 13.8 billion years.

The new report describes how Earendel was detected with the aid of gravitational lensing — a phenomenon in which a closely grouped (as seen from Earth) cluster of galaxies warps the space around it to magnify, distort and sometimes duplicate objects behind it. In this manner, the Hubble Space Telescope exploits a natural cosmic magnifier.

Large objects such as galaxies can be magnified several times over, but very small objects, like stars, can be magnified to an astonishing degree. “This star is magnified by a factor of thousands,” the report in Nature states.

Earendel is part of an early, small galaxy whose light has been magnified and distorted in two curved strips as a result of such lensing. Astronomer Dan Coe of Johns Hopkins discovered and named the Sunrise Arc in 2016 as part of a Hubble observation program. Welch, Coe’s student, scrutinized a tiny speck — some kind of object — providentially located on the arc where the magnification was highest. Over the course of 3½ years, the object remained in that spot.

Welch used computer models to compute the distance to the object. By 2020, he had begun to think this was something special, he said.

“We saw it, and at first I kind of figured it was just a very small star cluster,” Welch said. “The more I tried to model what its intrinsic properties might be, it just kept coming up that it was much smaller than a star cluster. Based on its brightness, it was more consistent with being a massive star.”

Other scientists weighed in. The single-star hypothesis remained persuasive, and the paper by Welch and his colleagues — the co-authors are scientists from 11 nations — made its way through peer review. (Publication in a prestigious journal such as Nature does not make something true but adds luster to the claim.)

“When we look back to these distances, most of the objects we see are just these little red smudges,” Coe said. “To be able to see an individual star at this distance — few really dared to dream we could see something like this.”

As with any object that far away in the universe, it is easier to say where it was than where it is. Earendel’s light is deeply redshifted, as are all cosmically distant objects. The degree to which the light has been shifted toward the red end of the spectrum is a cosmic yardstick, telling astronomers the distance to that object. Specifically, it is at redshift 6.2, which cosmologists will tell you is a really big redshift.

In the case of Earendel, astronomers calculate that its light has taken about 12.9 billion years to reach us. Thus, we see the object as it existed 12.9 billion years ago.

What was the fate of Earendel? Probably something explosive, followed by darkness. Most massive stars last only a few million years, or in some cases tens of millions, before exploding in a supernova. The bright blue stars that dominate the night sky as seen from Earth — Sirius and Rigel, for example — are young, hot stars, much brighter intrinsically than our own ancient, yellow sun, and with much shorter life spans.

If Earendel or its remnants collapsed into a black hole, then in theory it is still present in our universe, hidden in the far depths of space. Black holes stick around for a very long time.

When astronomers look at Earendel and the distorted, elongated galaxy named the Sunrise Arc, and then examine the other small galaxies of the deep past, they see a universe still getting its sea legs. The first stars and galaxies formed something like 300 million years after the big bang. Earendel is seen about 600 million years after that cosmic dawn. In that young cosmos, planets may have been rare, along with the heavy elements necessary for life as we know it. The universe may have been lifeless. It is very unlikely that any astronomers were on the scene.

“Galaxies were just starting to form around that time. So you wouldn’t have the big, beautiful spiral galaxies that we see nearby today. You would have had a lot of chaotic, clumpy galaxies,” Welch said.

One possibility is that Earendel is a hypothesized Population III star — one constituted entirely, or almost entirely, of hydrogen and helium, the primordial elements of the early universe. The heavier elements of the periodic table (things such as oxygen, carbon and iron) came along later, having been created within stars that exploded. Life as we know it is made of star stuff, a concept made famous by astronomer Carl Sagan.

The Webb is an infrared telescope, which allows it to penetrate the deepest realms of space and see the highly redshifted objects of the early universe. It has instruments that can discern the elemental composition of atmospheres around faraway planets — exoplanets — that orbit stars other than our sun.

In interviews this week, several scientists who are not part of the Earendel team praised the technical virtuosity of the discovery, noting that further observations could firm up the claim and potentially provide insights into the early evolution of stars.

“[T]he identification of this bright object as a single star is highly dependent on the models of the gravitational lens,” Heidi Hammel, vice president of science at the Association of Universities for Research in Astronomy, said in an email. She added that if the discovery is confirmed by observations with the Webb, “this will be a remarkable result that will give us insight into star formation at much greater distances than we have traditionally been able to access.”

Elena Sabbi, an astronomer at the Space Telescope Science Institute, noted in an email that no one has ever been able to see a Population III star, although they’ve been long hypothesized.

“These are the stars that changed forever the Universe from the cold and boring soup of hydrogen, helium and lithium to a place where planets capable of supporting complex forms of life can form,” she said.

Michael S. Turner, a University of Chicago cosmologist, said in an email that the Webb telescope “now has at least one target that isn’t an exoplanet, but is just as exciting. We are truly in a golden age of discovering our place in the Universe.”

via The Washington Post

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