No chance of flying too close to this: Icarus, the most distant star seen, is 9bn light years away

And you'll need more than wings to reach it

Icarus, a gigantic bright blue star, is the farthest such body yet discovered by astroboffins, the Space Telescope Science Institute announced on Monday.

The light emitted from the star takes a whopping nine billion years to reach Earth. It means that observers can see what Icarus looked like when the universe was about 30 percent of its current age, about 4.1 billion years old. It was only spotted by the Hubble Space Telescope thanks to the phenomenon of gravitational lensing.

Astronomers have been able to spot galaxies farther away than Icarus. In 2015, galaxy EGS8p7 was reported to be more than 13 billion years old, making it the most distant galaxy ever found. Faraway stars, however, are more difficult to make out.

“This is the first time we’re seeing a magnified, individual star," said study leader Patrick Kelly, an assistant astronomy professor at the University of Minnesota. 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 not a supernova, the researchers said. “The source isn’t getting hotter; it’s not exploding. The light is just being magnified. And that’s what you expect from gravitational lensing” Kelly added.


Icarus' brightness magnified in 2016 by gravitational lensing, allowing it to be seen by astronomers ... Image credit: NASA, ESA, and P. Kelly (University of Minnesota).

To see stars like Icarus, gravitational lensing is needed. It’s a phenomenon that occurs when the light emitted from a far-flung object passes by a cluster of massive galaxies to reach the observer. The gravitational field from the mass of the galaxies bends the light rays and acts as a magnifying glass, amplifying the light emitted from the object.

"Galaxy clusters have enormous masses, and the mass causes the paths of photons that pass near it to be deflected. A cluster can highly magnify a background source by sending a greater fraction of its photons towards the earth," Kelly explained to The Register.


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Icarus was made visible from the gravitational lensing effect produced by a galaxy cluster codenamed MACS J1149+2223 that lies five billion light years away. It is believed that when a star, with a similar mass to the Sun and part of one of the galaxies part of the MACS J1149+2223 cluster, moved in front of Icarus it made it 2,000 times brighter than normal.

If it wasn’t for the star, it is estimated that the mass from the foreground galaxy cluster would magnify the light to about 600 times, making it harder for the astronomers to pinpoint Icarus.

The researchers analysed the light from Icarus using NASA’s Hubble Space Telescope, and found that it was a blue supergiant star.

Kelly told El Reg, he hopes that finding older stars like Icarus will help scientists understand the nature and evolution of stars.

"I never imagined that we would be able to observe individual stars at such great distances. Until now, we have only been able to study the combined light from millions or billions of stars at once at such great distances.

"We should also be able to learn about the make-up of galaxy clusters by looking for fluctuations in the light curves of background stars. These could tell us about the nature of dark matter, and how massive stars evolve." ®

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