Free Astronomy Magazine May-June 2022

MAY-JUNE 2022 ASTRO PUBLISHING T he star nicknamed Earendel (indicated here with an arrow) is po- sitioned along a ripple in spacetime that gives it ex- treme magnification, al- lowing it to emerge into view from its host galaxy, which appears as a red smear across the sky. The whole scene is viewed through the distorted lens created by a massive galaxy cluster in the inter- vening space, which allows the galaxy’s features to be seen, but also warps their appearance—an effect as- tronomers call gravita- tional lensing. The red dots on either side of Earendel are a star cluster that is mirrored on either side of the ripple, a result of the gravitational lensing dis- tortion. The entire galaxy, called the Sunrise Arc, ap- pears three times, and knots along its length are other mirrored star clus- ters. Earendel’s unique po- sition right along the line of most extreme magnifi- cation allows it to be de- tected, even though it is not a cluster. [NASA, ESA, B. Welch (JHU), D. Coe (STScI), A. Pagan (STScI)] The two possible scenarios justify the efforts of different teams of as- tronomers in the search for Popula- tion III stars. Of all the teams active in this field, one particularly large group, led by Brian Welch (Depart- ment of Physics and Astronomy, Johns Hopkins University) and Dan Coe (Space Telescope Science Insti- tute), may have recently hit the mark. In fact, at the end of March, an article entitled “A highly magni- fied star at redshift 6.2” was pub- lished in Nature , which refers to the discovery of a star located 12.9 bil- lion light years from Earth, or in an epoch 900 million years after the Big Bang. This performance wipes out the previous record of the farthest star, set in 2018 at 9.4 billion light years, when the universe was about 4.4 billion years old. The protagonist of both discoveries was the Hubble Space Telescope, with the decisive help of the phe- nomenon of gravitational lensing. Here is a statement from Welch about the most recent discovery: “We almost didn’t believe it at first, it was so much farther than the pre- vious most distant, highest redshift star. Normally at these distances, en- tire galaxies look like small smudges, the light frommillions of stars blend- ing together. The galaxy hosting this star has been magnified and dis- torted by gravitational lensing into a long crescent that we named the Sunrise Arc.” The discovery was made by examin- ing data collected during Hubble’s Reionization Lensing Cluster Survey (RELICS) program, coordinated by Coe, which includes images of 41 galaxy clusters that generate gravi-