MACS J1149 Lensed Star 1, also known as Icarus, is a blue supergiant star observed through a gravitational lens. It is the most distant individual star to have been detected so far, at approximately 14 billion light-years from Earth. Light from the star was emitted 4.4 billion years after the Big Bang. According to co-discoverer Patrick Kelly, the star is at least a hundred times more distant than the next-farthest non-supernova star observed, SDSS J1229+1122, and is the first magnified individual star seen.
History
In April and May 2016, the bluesupergiant star was found in the course of studying the supernovaSN Refsdal with the Hubble Space Telescope. Astronomer Patrick Kelly of the University of Minnesota is the lead author of the finding, published in the journal Nature Astronomy. While astronomers had been collecting images of this supernova from 2004 onward, they recently 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. The galaxy cluster magnification is probably by a factor of ≈600, while the microlensing event, which peaked in May 2016, brightened the image by an additional factor of ≈4. There was a second peak near the brightness curve maximum, which may indicate the star was binary. The microlensing body may have been a star or a black hole in the cluster. Continuous monitoring of the star Icarus may one day rule out the possibility that primordial black holes constitute a sizable fraction of dark matter. Normally, the only astronomical objects that can be detected at this range would be either whole galaxies, quasars, or supernovas, but the light from the star was magnified by the lensing effect. They determined the light was from a stable 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 emitted when the universe was about 30% 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 discovery shows that astronomers can study the oldest stars in background galaxies of the early universe by combining the strong gravitational lensing effect from galaxy clusters with gravitational microlensing events caused by compact objects in these galaxy clusters. By using these events, astronomers can study and test some models about dark matter in galaxy clusters and observe high energy events in young galaxies.
