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Hubble discovers the furthest star ever observed


The light of a star that lived during the first billion years after the universe’s origin in the big bang has been detected by NASA’s Hubble Space Telescope, making it the furthest individual star ever observed to date.

The discovery represents a significant step back in time from the previous single-star record holder, which was discovered by Hubble in 2018. That star existed when the universe was around 4 billion years old, or 30 percent of its present age, a period known as “redshift 1.5” by astronomers. Scientists use the term “redshift” to describe how light from faraway objects is stretched or “shifted” to longer, redder wavelengths as it travels toward us as the cosmos expands.


The newly discovered star is so far away that its light has taken 12.9 billion years to reach Earth, arriving to us at redshift 6.2, when the universe was just 7% of its present age. Clusters of stars nested inside early galaxies are the tiniest things hitherto discovered at such a long distance.


“We almost didn’t believe it at first because it was so far out from the previous most-distant, greatest redshift star,” said astronomer Brian Welch of Johns Hopkins University in Baltimore, lead author of the study revealing the finding, which was published on March 30 in the journal Nature. The finding was found using data from Hubble’s RELICS (Reionization Lensing Cluster Survey) program, which was conducted by co-author Dan Coe at the Space Telescope Science Institute (STScI), which is also located in Baltimore.


“At these distances, whole galaxies seem like little smudges, with the light from millions of stars mixing together,” Welch said. “Gravitational lensing enlarged and warped the galaxy harboring this star into a lengthy crescent that we termed the Sunrise Arc.”


Welch concluded that one aspect of the galaxy is an extraordinarily magnified star he named Earendel, which means “dawn star” in Old English. The finding has the potential to usher in a hitherto unknown period of extremely early star creation.

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“Because Earendel lived so long ago, it may not have had all of the same basic ingredients as the stars surrounding us now,” Welch stated. “Studying Earendel will provide us with a window into a time in the cosmos that we are unfamiliar with, but which led to everything we know today. It’s like if we’ve been reading a great intriguing book, but we just got to the second chapter, and now we’ll get to see how it all began “Welch said.


When the Planets Align


According to the researchers, Earendel is at least 50 times the mass of our Sun and millions of times brighter, rivaling the most massive stars known. But even such a dazzling, extremely high-mass star would be hard to detect at such a long distance without the natural amplification provided by WHL0137-08, a massive galaxy cluster located between us and Earendel. The galaxy cluster’s bulk warps the fabric of space, generating a strong natural magnifying glass that distorts and considerably amplifies light from distant objects behind it.


The star Earendel appears directly on, or quite near to, a ripple in the fabric of space due to an unique alignment with the magnifying galaxy cluster. This ripple, known as a “caustic” in optics, gives maximal magnification and brightness. On a sunny day, the rippling surface of a swimming pool creates patterns of dazzling light on the bottom of the pool. The surface ripples work as lenses, focusing sunlight to maximum brightness on the pool bottom.


Because of this caustic, the star Earendel stands out from the ambient brilliance of its parent galaxy. Its radiance is multiplied a thousand times or more. At the moment, scientists are unable to tell if Earendel is a binary star, despite the fact that most big stars have at least one smaller partner star.

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Webb’s confirmation


Astronomers anticipate that Earendel will continue to be greatly amplified for many years to come. NASA’s James Webb Space Telescope will observe it. Webb’s exceptional sensitivity to infrared light is required to learn more about Earendel because the universe’s expansion causes its light to be stretched (redshifted) to longer infrared wavelengths.


“We intend to confirm Earendel is a star, as well as measure its brightness and temperature, using Webb,” Coe added. These specifics will help to identify its kind and stage in the stellar lifetime. “We also anticipate to detect a paucity of heavy elements in the Sunrise Arc galaxy, which originate in future generations of stars. This would imply that Earendel is a rare, huge, metal-deficient star “Coe said.


Astronomers will be fascinated by Earendel’s composition since it originated before the cosmos was filled with the heavy elements created by successive generations of huge stars. If further research reveals that Earendel is exclusively made up of primordial hydrogen and helium, it would be the first evidence for the mythical Population III stars, which are thought to be the very first stars to form after the big bang. While the likelihood is low, Welch acknowledges it is appealing nevertheless.


“With Webb, we may be able to view stars even farther away than Earendel, which would be incredible,” Welch added. “We’ll go back as far as we can. I’d want to see Webb shatter Earendel’s long-distance record.”


The Hubble Space Telescope is a NASA-ESA international collaboration project (European Space Agency). The telescope is managed by NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Hubble scientific operations are managed by the Space Telescope Science Institute (STScI) in Baltimore, Maryland. The Association of Universities for Research in Astronomy in Washington, D.C. manages STScI for NASA.

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