The Hubble Space Telescope has broken yet another observing record: The famed observatory has found the most distant “ordinary” star ever observed, at an astounding 9 billion light-years from Earth — which means the light scientists see started traveling at least 9 billion years ago. By comparison, the age of the universe is roughly 13.8 billion years.
Normally, stars that far away are too difficult to make out individually; a galaxy or a supernova (star explosion) is much easier to see.
But this particular star ICARUS — classified as an ordinary star, meaning a star on the main sequence of evolution that is fusing hydrogen into helium — came to light thanks to a rare alignment, researchers reported in a new study.
When a main sequence star ceases burning the hydrogen at its core, it leaves the main sequence. This leads to a range of different outcomes for stars. Commonly, larger stars off the main sequence explode into supernovas, while smaller stars collapse into white dwarfs.
Astronomers found the star, which is nicknamed Icarus, through gravitational lensing. This phenomenon refers to how a massive galaxy cluster or other objects can bend light from objects behind it, making dim objects much brighter from Earth’s perspective.
Usually, this lensing process can magnify objects by up to 50 times, but astronomers got lucky here: The newfound star was magnified more than 2,000 times because a star was briefly passing through the line of sight between Hubble and Icarus, researchers said in a statement from the University of California, Berkeley.
This rare glimpse of a faraway star could provide a window into how stars, in general evolve, especially those that are extremely luminous, the team 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,” lead study author Patrick Kelly said in the statement. Kelly was a postdoctoral scholar at the University of California, Berkeley when he worked on the research but is currently on the faculty at the University of Minnesota.
ICARUS, Most Distance Star Ever Seen.
Icarus, known more formally as MACS J1149 Lensed Star 1 (LS1), showed up as Kelly was following up on a supernova, called SN Refsdal, that he discovered in 2014. The supernova was discovered using a gravitational lens in the constellation Leo; the lens was formed by a galaxy cluster known as MACS J1149+2223.
“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,” study co-author Alex Filippenko, an astronomer at UC Berkeley, said in the same statement. These lenses are amazing cosmic telescopes.”
Kelly’s team examined the colors coming from Icarus’ light and found that it was a blue supergiant. This kind of star is more massive and larger than our sun, shining up to hundreds of thousands of times brighter. Still, Icarus was so far away that astronomers would never have spotted it without powerful lensing. Kelly suspected the star was far more magnified than the supernova — a hypothesis later borne out by modeling.