With Giant Lens, Astronomers Find a Single Star Across Half the Universe

Through a lucky quirk of nature, astronomers have used the Hubble Space Telescope to view a single star halfway across the universe. Nine billion light years from Earth, the giant blue-white star, nicknamed “Icarus” by the team, is by far the most distant individual star ever seen.

Distant star image

Icarus is the farthest individual star ever seen. It is only visible because it is magnified by the gravity of a massive galaxy cluster, located about 5 billion light-years from Earth. The panels at right show the view in 2011, without Icarus visible, and the star’s brightening in 2016. (Hubble/STScI)

“This is the first time we’re seeing a magnified, individual star,” said study leader Patrick Kelly of the University of Minnesota, Twin Cities. “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.”

Marusa Bradac, a physics professor and astronomer at UC Davis and graduate student Austin Hoag are part of the team describing Icarus and another distant, magnified star in two papers published April 2 in the journal Nature Astronomy.

Hubble was able to see Icarus because a gigantic magnifying glass happened to float in front of it. The magnifier is galaxy cluster MACS J1149+2223, about five billion light years from Earth. MACS J1149’s gravitational field bends light, magnifying some objects behind it.

The team had been using the Hubble Space Telescope to monitor a supernova – a giant exploding star – in a distant spiral galaxy when they noticed another nearby object suddenly increasing in brightness. Like the mythological Icarus who flew too close to the Sun, the star had a brief moment of glory, rocketing to about two thousand times its normal brightness as seen from Earth.

The astronomers could tell that Icarus was not another supernova because it did not get hotter, just brighter. The colors of light coming from the object show that it is a blue-white supergiant star. Although Icarus is much bigger, hotter and brighter than our Sun, without the lensing effect it would still be invisible at such a tremendous distance.

The other transient star observed, nicknamed “Spock,” is closer to Earth, but also became visible through a gravitational lens.

The astronomers could even measure a “twinkling” effect in the light from these stars. They concluded that Spock’s twinkling was caused by explosions on the star’s surface, while Icarus is twinkling because of the relative motion between it and the Earth.

These stars did allow the team to test one theory about the nature of the dark matter thought to make up much of the universe. This particular theory holds that dark matter – which is effectively invisible except for its gravitational pull – is made up of swarms of black holes that formed at the beginning of the universe. Data from the new observations, though, do not support this idea.

Astronomers hope to find many more such gravitationally lensed stars when the James Webb Space Telescope is launched and in operation. They might even be fairly common, if we have the tools to look for them.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.

More information

Hubble Uncovers the Farthest Star Ever Seen (STScI news release)

Extreme magnification of an individual star at redshift 1.5 by a galaxy-cluster lens (Nature Astronomy)

Two peculiar fast transients in a strongly lensed host galaxy (Nature Astronomy)


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