Hubble telescope sees star 9 billion light-years away via gravitational lens

Astronomers from the American Berkeley University have detected a star about nine billion light-years from Earth using the Hubble Space Telescope through a gravitational lens. This makes it the farthest star ever detected.

According to one of the astronomers, the discovered star is at least a hundred times as far away as the second most distant individual star that can be studied. The discovery of this star, dubbed Icarus, is quite unusual, as it is so far away that it would normally go unnoticed. Only very bright objects, such as supernovas or galaxies, can still be detected at distances of nine billion light-years from Earth.

The discovery of Icarus, made in 2016, was made possible by the gravitational lensing action of a cluster of galaxies located five billion light-years from Earth. Such clusters typically give a 50-fold gain, but a specific star in the cluster provided a brief gain of 2,000 times.

Individual stars or galaxies can amplify the light from trailing stars if they line up exactly, acting like a lens. The passing star caused a so-called Einstein ring with its gravity, a kind of ring of light that is bent around the object by gravity, as it were. This ring is too small to be detected, but the effect boosted the star’s brightness, making it visible.

Located in a spiral galaxy, the researchers say Icarus is a so-called blue superstar that is much larger, heavier, hotter and probably a hundred to several thousand times brighter than our sun. The astronomers believe that the star’s light will be magnified even more over the next decade as clusters of stars pass more frequently in front of Icarus, possibly amplifying about 10,000 times.

The discovery is published in the scientific journal Nature Astronomy, under the title ‘Extreme magnification of an individual star at redshift 1.5 by a galaxy-cluster lens’.

The square on the left shows the cluster of galaxies called MACS J1149+2223. Straight is Icarus, or MACS J1149+2223 Lensed Star 1, which was not visible in 2011 but was visible in 2016.