Free Astronomy Magazine May-June 2018

51 MAY-JUNE 2018 SPACE CHRONICLES in the star’s brightness, produced by the microlens brought about by the gravitational effect of stars belong- ing to the cluster. Although its official designation is MACS J1149+2223 Lensed Star 1, the team decided to name the star after the character in Greek mythology who flew too close to the Sun with wings and feathers made of wax. Just like Icarus, the light from this star, on its journey towards Earth, passed so close to a Sun-like star in the intergalactic region of the MACS J1149+2223 cluster that its bright- ness was amplified by a factor of about 2000, thus attaining the glory of its Greek namesake. “We were able to establish that Icarus is a blue supergiant star, a type of star that is much bigger, more massive, hotter and possibly thousands of times brighter than the Sun. But, at its great distance, it would be impossible to observe it as an indi- vidual star, even with the Hubble, were it not for the gravitational lens phenomenon,” com- ments Ismael Pérez Fournon. Pablo Pérez González (UCM) explains, “Until 2016 it was only possible to observe individual stars in galaxies close to the Milky Way. Today, we are witnessing an in- dividual star, very like Rigel, which is halfway across the Universe, and which, indeed, no longer exists.” The detection of Icarus with the Hubble was so extraordinary that, when it was discovered, telescopes worldwide started to observe it. In Spain, special observing time was applied for on the Gran Telescopio Canarias (GTC), the largest optical- infrared telescope in the world. It turned out, according to Pérez González, that the GTC “was the known as ‘gravitational lensing’. The gravity of an extremely massive clus- ter of galaxies acts like a giant cos- mic magnifying glass that amplifies the light from the most distant ob- jects. The gravitational lens that has enabled us to see Icarus is created by the galaxy cluster known as MACS J1149+2223, located some 5000 mil- lion light years from Earth. Combining this lens with Hubble’s resolution and sensitivity has en- abled an analysis to be performed of this distant star. The research team that has partici- pated in this study includes, among other workers, José M. Diego of the Instituto de Física de Cantabria (IFCA), Steven Rodney of the Univer- sity of South Carolina, Columbia (USA), Pablo G. Pérez González of the Universidad Complutense de Madrid (UCM), Tom Broadhurst of the University of the País Vasco (UPV), and Ismael Pérez Fournon (IAC and ULL). Patrick Kelly and his coworkers detected sudden changes only telescope to detect this star so distant from Earth, given that Icarus is so faint.” The discovery of Icarus is exceptional not only in terms of the detection of such a distant star. Detecting the amplification of an individual star’s brightness enables us to study the nature of the cluster’s dark matter content, thus putting to the test a theory of the nature of the dark matter of the cluster that shows that most of it is in the form of primor- dial black holes. According to José M. Diego (IFCA), first author of the theoretical paper accompanying the Nature Astronomy article, “If the dark matter consisted of black holes similar to those detected by LIGO (Laser Interferometer Gravitational- Wave Observatory), the signal ob- served from Icarus would have been very different, which enables us to discard these types of candidates.” Tome Broadhurst (UPV) adds, “this type of study will in future enable us to set limits on other dark matter models, such as those that postulate superlight particles of matter and their quantum effects.” Also, in May 2016, another image appeared next to Icarus that seems to suggest that we are not dealing with an individual star. We could in- stead be talking about a binary sys- tem, with two stars in orbit around each other. A rtistic simulation of Icarus (MACS J1149+2223 Lensed Star 1). [Gabriel Pérez, SMM (IAC)] !