Hubble telescope spots Earendel, the most distant star seen to date

31 Mar 2022

The star Earendel (indicated with an arrow) is positioned along a ripple in spacetime that gives it extreme magnification, allowing it to emerge into view from its host galaxy, which appears as a red smear across the sky. Image: NASA, ESA, B Welch (JHU), D Coe (STScI), A Pagan (STScI)

Astronomers said the discovery could help open up knowledge on an uncharted era of very early star formation.

The Hubble Space Telescope has broken records by spotting the light of a star that existed within the first 1bn years after the Big Bang.

The primordial star called Earendel – which means ‘morning star’ in old English – is so far away that it took 12.9bn years for its light to reach Earth, making it the farthest individual star ever seen.

The star appears to us as it did when the universe was only 7pc of its current age, in a period known by astronomers as ‘redshift 6.2’. Scientists use the term redshift because as the universe expands, light from distant objects is stretched.

This discovery is a huge leap from the previous record holder, Icarus, which was discovered by NASA and the European Space Agency’s Hubble telescope in 2018. That star existed when the universe was around 4bn years old, or 30pc of its current age.

The lead author of the paper describing the discovery, astronomer Brian Welch, said the team “almost didn’t believe” the discovery at first.

“Normally at these distances, entire galaxies look like small smudges, with the light from millions of stars blending together,” Welch said. “The galaxy hosting this star has been magnified and distorted by gravitational lensing into a long crescent that we named the Sunrise Arc.”

Galactic magnification

The research team estimates that Earendel is at least 50 times the mass of our sun and millions of times brighter. However, the star still would have been impossible to see without the aid of a huge galaxy cluster between us and Earendel.

This galaxy cluster – known as WHL0137-08 – is so large that its mass warps the fabric of space, creating a natural magnifying effect that amplifies the light of distant objects behind it. Astronomers expect this magnification of Earendel to continue for years thanks to a rare alignment.

Following this discovery, Earendel will be observed by the James Webb Space Telescope, which was launched on 25 December 2021. As the successor to Hubble, it is the largest and most powerful space observatory ever built and is set to give scientists a new eye on the cosmos.

The James Webb telescope’s high sensitivity to infrared light is needed to learn more about Earendel, such as its brightness and temperature.

“Earendel existed so long ago that it may not have had all the same raw materials as the stars around us today,” Welch said. “Studying Earendel will be a window into an era of the universe that we are unfamiliar with, but that led to everything we do know.”

Investigating Earendel could also help confirm the existence of ‘Population III’ stars, which are hypothesised to be the very first stars born after the Big Bang made up of primordial hydrogen and helium. Although Welch said the probability for this is small.

“With Webb, we may see stars even farther than Earendel, which would be incredibly exciting,” Welch added. “We’ll go as far back as we can. I would love to see Webb break Earendel’s distance record.”

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Leigh Mc Gowran is a journalist with Silicon Republic