Washington: NASA’s Hubble Space Telescope has discovered the farthest individual star ever seen an enormous blue stellar body nicknamed Icarus located over halfway across the universe. In a study published in Nature Astronomy, an international team of researchers announced the discovery of the most distant star ever observed.
The team detected the blue supergiant star — which shone when the universe was just one-third its current age — with the help of both the Hubble Space Telescope and an observational phenomenon known as gravitational lensing.
The unique discovery not only provides astronomers with insight into the formation and evolution of stars in the early universe, but also the composition of galaxy clusters, and even the very nature of dark matter itself.
The light from the record-breaking star, which the team has since nicknamed Icarus, was emitted just 4.4 billion years after the Big Bang. Although the star was undoubtedly bright, being located at such a great distance away would have typically made it impossible to view, even with our most powerful telescopes.
Gravitational lensing is an effect that is predicted by Einstein’s general theory of relatively. It occurs when diverging light rays from a distant object are bent back inward, or lensed, as they pass by an extremely massive object, such as a galaxy cluster.
According to the study, when a galaxy cluster serendipitously wanders directly between Earth and a distant background object, gravitational lensing can magnify the distant object by up to a factor of about 50. Furthermore, if there is a smaller, impeccably aligned object within the lensing galaxy cluster, then the background object can be magnified (in a process called gravitational microlensing) by a factor of up to 5,000.
The star, harboured in a very distant spiral galaxy, is so far away that its light has taken nine billion years to reach Earth. It appears to us as it did when the universe was about 30% of its current age.
Normally, the star would be too faint to view, even with the world’s largest telescopes.
However, through a phenomenon called gravitational lensing that tremendously amplifies the star’s feeble glow, astronomers were able to pinpoint this faraway star and set a new distance record.
Located about 5 billion light-years from Earth, this massive cluster of galaxies sits between the Earth and the galaxy that contains the distant star.
By combining the strength of this gravitational lens with Hubble’s exquisite resolution and sensitivity, astronomers can see and study Icarus.
The team – including Jose Diego of the Instituto de Fisica de Cantabria in Spain, and Steven Rodney of the University of South Carolina in the US – dubbed the star Icarus, after the Greek mythological character who flew too near the Sun on wings of feathers and wax that melted.
Detecting the amplification of a single, pinpoint background star provided a unique opportunity to test the nature of dark matter in the cluster.
Dark matter is an invisible material that makes up most of the universe’s mass.
By probing what is floating around in the foreground cluster, scientists were able to test one theory that dark matter might be made up mostly of a huge number of primordial black holes formed in the birth of the universe with masses tens of times larger than the Sun.
The results of the test disprove that hypothesis, because light fluctuations from the background star, monitored with Hubble for 13 years, would have looked different if there were a swarm of intervening black holes.
Furthermore, the newly discovered star may also help shed light on one of the most mysterious materials in our universe — dark matter. “If dark matter is at least partially made up of comparatively low-mass black holes, as it was recently proposed, we should be able to see this in the light curve of [Icarus],” said Kelly. “Our observations do not favor the possibility that a high fraction of dark matter is made of these primordial black holes with about 30 times the mass of the Sun.”
No matter what astronomers are able to glean from the distant Icarus, this chance discovery of an extremely distant and magnified star is not likely to be the last. With the upcoming launch of modern, more-powerful telescopes like the James Webb Space Telescope, astronomers are optimistic that microlensing events like this may allow them to study the evolution of the universe’s earliest stars in unprecedented detail.