This point of light marked with an arrow is a real sensation. Because it comes from the most distant and thus earliest ever observed star in the universe.
The star, christened “Earendel” after the Old English word for morning star, shone as early as 12.9 billion years ago and thus at a time only around 900 million years after the Big Bang. “At these distances, galaxies usually resemble mere patches of light that combine the light from millions of individual stars,” explains Brian Welch from Johns Hopkins University in Baltimore. Individual stars, on the other hand, are usually far too faint to be visible over such distances.
But a cosmic stroke of luck came to the rescue of the astronomers around Welch: a foreground galaxy pushed in front of Earendel’s home galaxy in such a way that its gravity acted like a strong lens. This distorted the galaxy into a long arc, and also amplified and magnified the star. Because its light is magnified between 1,000 and 40,000 times, Earendel is visible as a point of light amidst the faint arc in this Hubble Space Telescope image.
“We couldn’t believe it because it’s so much further away than the most distant known star,” says Welch. Earendel dates from the early days of the cosmos and may have belonged to one of the first generations of stars. Their formation ended the “dark age” of the universe, which lasted several hundred million years after the Big Bang and when there were no stars or galaxies.
The newly discovered star could thus provide valuable insights into the first stars in the universe. “Earendel existed so long ago that it didn’t have the same raw materials as today’s stars,” says Welch. Because most of the chemical elements only came about over time through nuclear fusion inside early stars and their supernovae. Astronomers therefore assume that the first generation of stars consisted only of hydrogen and helium – the elements formed in the Big Bang.
The astronomers could get the chance for closer studies of Earendel already this summer. Because then the James Webb Space Telescope will start its scientific operation. Its high-resolution infrared optics are particularly well suited to capturing the light of such early stars and analyzing it spectroscopically. “Using the James Webb telescope, we can then unequivocally confirm that Earendel is indeed a star and measure its brightness and temperature more accurately,” explains co-author Sune Toft from the Niels Bohr Institute at the University of Copenhagen.