Image of Icarus, outlined in a white box. Image: NASA, ESA and Dr Patrick Kelly
NASA and ESA’s Hubble telescope unveils distant star Icarus, thanks to gravitational lensing.
A tiny dot of light in a photograph captured by the Hubble space telescope is the most distant individual star ever seen that is not a supernova.
Discovery of Icarus
Dr Patrick Kelly of the University of Minnesota, first author of the research published in Nature Astronomy, said: “We are looking back three-quarters of the way almost to the Big Bang.”
The team has dubbed the star Icarus but its official moniker is MACS J1149.5+223 Lensed Star 1.
Researchers say the light was emitted from the star when it was more than 9bn light years from Earth. It is now even further away but will have died, becoming either a neutron star or a black hole.
Normally, stars at such a distance away are too faint to be identified on an individual basis, but a rare cosmic alignment meant astronomers were able to capture these images of the most distant normal star ever observed.
A chance discovery
In 2016, the team was examining a supernova called SN Refsdal in a galaxy more than 9bn light years away when it noticed a pinprick of light that appeared four times as bright than in previous images. The light seemed to come from an object in the same galaxy as SN Refsdal and appeared in the area of a well-known galaxy cluster 5bn light years from Earth.
Study co-author Dr Mathilde Jauzac said: “As we monitored the cluster due to SN Refsdal, we obtained imaging of the cluster regularly and we saw the Icarus region brightening up.”
What is gravitational lensing?
Gravitational lensing – the phenomenon that helped to spot Icarus – had been used to study distant galaxies, but Icarus shows there are opportunities to apply it to individual stars.
In writing about the phenomenon, the researchers said: “The bending of light by massive galaxy clusters in the line of sight can magnify the distant universe and make dim, far-away objects visible.” In basic terms, this is when light emitted by a star is bent by the gravitational effect of objects in front of it.
Dr Kelly added: “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.”
Icarus is what is known as a blue supergiant, which is much larger and hotter than our own sun.
New study possibilities uncovered
Study co-author Alex Filippenko, an astronomer at the University of California, Berkeley, said: “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.”
He added: “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 9bn light years.”
The astronomy team also used Icarus to test and reject one theory of dark matter – that it consists of numerous primordial black holes hiding inside galaxy clusters – and to probe the make-up of normal matter and dark matter inside the galaxy cluster.
