Hubble spots the farthest star

Officially designated MACS J1149+2223 Lensed Star 1 (nicknamed Icarus), this star is the farthest ever seen. Now, we’ve seen galaxies further away (with stars within them) – but this is the farthest we’ve ever seen a single star.

The little pinpoint of light seen below was captured by the Hubble in 2016. That light spent the better part of 9 billion years traveling towards Earth.

Icarus star

You’ll notice how Icarus doesn’t show up in the 2011 image. That’s because even though it’s a blue supergiant star (possibly hundreds of thousands of times brighter than our Sun), it’s way too far away to show up in a traditional Hubble image. What’s happening here is a phenomenon astronomers have dubbed ‘gravitational lensing.’ Imagine a cosmic microscope amplifying the star’s light by 2000 times.

In this case, the cosmic microscope is a galaxy cluster called MACS J1149+2223. Situated about 5 billion light-years from Earth, this enormous cluster of galaxies was positioned between Earth and Icarus in 2016. Light from Icarus was bent and amplified by the galaxy cluster towards Earth.

Here’s a short video showing how gravitational lensing works.

Stumbling upon Icarus

The team of researchers responsible for the Icarus discovery were not even looking for it. They were using the Hubble to keep tabs on a supernova in a distant spiral galaxy. In 2016, they noticed the new point of light in the image above. Was it another supernova? Maybe a distortion causing the same supernova to appear again?

Once the researchers started analyzing the colors coming from the object, they realized they were looking at a blue supergiant star. You’ve seen one before. Rigel, the brightest star in the constellation Orion, is a blue supergiant.

“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,” said Alex Filippenko, a professor of astronomy at UC Berkeley and one of the co-authors of the paper. “These lenses are amazing cosmic telescopes.”

Researchers also used the Icarus discovery to test a theory about dark matter. One theory suggests dark matter is mostly made up of a vast collection of primordial black holes formed right after the universe formed.

“The results of this unique test disfavor that hypothesis, because light fluctuations from the background star, monitored with Hubble for 13 years, would have looked different if there were a swarm of intervening black holes,” according to NASA.

Soon, Hubble will pass the torch to the James Webb Space Telescope. Discoveries like Icarus are expected to become much more frequent, and the James Webb Space Telescope should be able to tease out even more details about these far-flung stars.