Hubble has racked up a lot of firsts since its deployment in 1990. Now it has discovered one of its biggest accomplishments. The telescope looked back 12.9 billion years into the past to discover the most distant start ever found.
The star, nicknamed “Earendel”, an Old English word which means “rising light” or “morning star”, is technically named WHL0137-LS and dates back to less than one billion years after the universe's birth. The star’s light, as appears today, is that of when the universe was approximately 900 million years old, just 7% of its current age. The research team calculates that the star is at least 50 times as massive as our Sun, possibly up to 500 times more massive, and millions of times as bright.
"We almost didn't believe it at first, it was so much farther than the previous most-distant, highest redshift star," said astronomer Brian Welch of the Johns Hopkins University in Baltimore, lead author of the paper describing the discovery, which was published in the March 30 journal Nature. "Normally at these distances, entire galaxies look like small smudges, with the light from millions of stars blending together. The galaxy hosting this star has been magnified and distorted by gravitational lensing into a long crescent that we named the Sunrise Arc."
Gravitational lensing is only visible in rare cases and only the best telescopes can observe the related phenomena. As the light emitted by distant galaxies passes by massive objects in the universe, as Einstein predicted in his Theory of General Relativity, the gravitational pull from these objects can distort or bend the light.
Galaxies magnified several times are routinely discovered by way of this method. But in an astounding coincidence, the galaxies in a cluster named WHL0137-08 happened to line up in such a way as to focus the light of a single star toward us, magnifying its light thousands of times.
"As we peer into the cosmos, we also look back in time, so these extreme high-resolution observations allow us to understand the building blocks of some of the very first galaxies," said Victoria Strait, postdoc at the Cosmic Dawn Center, Copenhagen, and a collaborator and co-author of the study. “When the light that we see from Earendel was emitted, the Universe was less than a billion years old. At that time it was four billion light-years away from the proto-Milky Way, but during the almost 13 billion years it took the light to reach us, the universe has expanded so that it is now a staggering 28 billion light-years away.”
Hubble's sensitivity and high resolution allow it to see faint and distant gravitational lenses that cannot be detected with ground-based telescopes whose images are blurred by the Earth's atmosphere. The gravitational lensing results in numerous images of the original galaxy each with a characteristically distorted banana-like shape or even into rings.
The find is a considerable leap beyond Hubble's previous distance record, in 2018, when it identified “Icarus,” a star that formed around four billion years after the Big Bang.
Astronomers expect that Earendel will remain highly magnified for years to come, giving the James Webb Space Telescope plenty of time to take its turn at a gander. Earendel's composition will be of great importance for astronomers, because it developed before the universe was filled with the heavy elements produced by successive generations of massive stars. If follow-up studies discover that Earendel is only made up of primordial hydrogen and helium, it would be the first proof for the legendary Population III stars, which are hypothesized to be the very first stars born after the big bang.
"With James Webb, we will be able to confirm that Earendel is indeed just one star, and at the same time quantify which type of star it is,” says Sune Toft, leader of the Cosmic Dawn Center and professor at the Niels Bohr Institute. “Webb will even allow us to measure its chemical composition. Potentially, Earendel could be the first known example of the Universe's earliest generation of stars.”