MACS J1149 Lensed Star 1, also known as Icarus, MACS J1149 Lensed Star 1 (LS1) and MACS J1149+2223 Lensed Star-1, is a blue supergiant star, and is currently the most distant star ever found, at approximately 9 billion light years away from Earth (redshift z=1.49) as of April 2018. Light from the star was emitted 4.4 billion years after the Big Bang. According to the co-discoverer Patrick Kelly, this star is at least a hundred times more distant than the next-farthest non-supernova star, SDS J1229+1122, and is the first time a magnified individual star has been observed.
The star was found in the course of studying the supernova SN Refsdal with the Hubble Space Telescope. While they had been collecting images of this nova from 2004 onward, they discovered a point source that had appeared in their 2013 images, and become much brighter by 2016. They determined that the point source was a solitary star being magnified more than 2,000 times by gravitational lensing. The light from LS1 was magnified not only by the huge total mass of the galaxy cluster MACS J1149+2223, located 5 billion light-years away, but also transiently by another compact object of about three solar masses within the galaxy cluster itself that passed through the line of sight, an effect known as gravitational microlensing. Normally, the only astronomical objects that can be detected at this range would be either whole galaxies or supernovas, but the light from the star was magnified by the microlensing effect. They determined the light was a star and not a supernova as its temperature did not fluctuate; the temperature also allowed them to catalog the star as a blue supergiant.
The light observed from the star was generated when the universe was about 1/4 of its current age of 13.8 billion years. Kelly suggested that similar microlensing discoveries could help them identify the earliest stars in the universe. The star does not exist as a blue supergiant anymore, given the known lifetime of such stars.
While Kelly had wanted to name the star Warhol, alluding to Andy Warhol's notion of having 15 minutes of fame, the team ended up naming the star Icarus instead, based on the mythological figure.