A blue “supergiant” nine billion light years away is the most distant single star ever to be observed by astronomers.
Usually at such distances scientists can only image galaxies, collections of billions of stars such as our own Milky Way, or supernovas and gamma ray bursts, colossal cosmic explosions.
Beyond about 100 million light years it is impossible to make out individual stars even with the most powerful telescopes.
In this case, a rare cosmic alignment naturally magnified the supergiant more than 2,000 times, allowing astronomers to see it.
The B-type blue supergiant star, hundreds or even thousands of times brighter than the sun, was discovered in Hubble Space Telescope images taken over the course of a year between April 2016 and 2017.
It could only be seen because of an effect called “gravitational lensing” that occurs when massive galaxy clusters bend the light of objects behind them.
In effect the galaxies act as a magnifying glass that can render dim far away objects visible.
The lensing phenomenon, predicted by Albert Einstein, is the result of a massive object bending space-time around it and forcing light beams to take a curved path.
Lead scientist Dr Patrick Kelly, who worked on the observations while at the University of California at Berkeley, US, said: “You can see individual galaxies out there, but this star is at least 100 times farther away than the next individual star we can study, except for supernova explosions.”
The star has the long formal name MACS J1149 Lensed Star 1 (LS1), but has been dubbed “Icarus” by the astronomers.
A report on its discovery appears in the journal Nature Astronomy.
Co-author Professor Alex Filippenko, also from the University of California at Berkeley, said: “For the first time ever we’re seeing an individual normal star, not a supernova, not a gamma ray burst, but a single stable star, at a distance of nine billion light years.
“These lenses are amazing cosmic telescopes.”
He added that other gravitational lensing alignments should allow more distant stars to be studied.
“There are alignments like this all over the place as background stars or stars in lensing galaxies move around, offering the possibility of studying very distant stars dating from the early universe, just as we have been using gravitational lensing to study distant galaxies,” said Prof Filippenko. “For this type of research, nature has provided us with a larger telescope than we can possibly build.”