Free Astronomy Magazine May-June 2022

MAY-JUNE 2022 T his graphic shows a timeline of the universe, stretching from the present day (left) all the way back to the Big Bang (right). The position of the record- breaking galaxy GN-z11 is shown not far from where the first stars began to form. The previous record holder’s position is also identified. [NASA, ESA, P. Oesch and B. Robertson (University of California, Santa Cruz), and A. Feild (STScI)] T his detailed view highlights the star Earendel’s position along a ripple in space-time (dotted line) that magnifies it and makes it possible for the star to be detected over such a great distance — nearly 13 billion light-years. Also indicated is a cluster of stars that is mirrored on either side of the line of mag- nification. The distortion and magnification are created by the mass of a huge galaxy cluster located in between Hubble and Earendel. The mass of the galaxy cluster is so great that it warps the fabric of space. Looking through that space is like looking through a magnifying glass — along the edge of the glass or lens, the appearance of things on the other side are warped as well as magni- fied. [Science: NASA, ESA, Brian Welch (JHU), Dan Coe (STScI). Image process- ing: NASA, ESA, Alyssa Pagan (STScI)] tational lenses. The attention of the researchers focused on a particular image of a remote galaxy, deformed in a 15” long arc (the aforemen- tioned “Sunrise Arc”) by the lensing produced by a galaxy cluster called WHL0137-08. After studying in de- tail the image of the galaxy (cata- loged WHL0137-zD1), the team came to the conclusion that one of its most compact structures could only be a star, whose light is ex- tremely intensified by the gravita- tional lens. The researchers decided to give that star an evocative name, Earendel, which in Old English (5 th - 12 th century) means “morning star” or “rising light.” In most cases, gravitational lensing intensifies the light of remote ob- jects by a few times, since the Earth- lens-remote object alignment is far from perfect; but the closer you get to optimal alignment, the greater the intensification of the light is (and, therefore, of the image). In Earendel’s case, a particularly favor- able alignment and the roughly point-like appearance of the star have meant that its brightness is in- tensified by thousands of times, making it observable with instru- ments that could never see it di- rectly. Although galaxy clusters deform space(time) in an inhomogeneous way that reflects the distribution of masses within them, there is still an intensification line or, more techni- cally, a critical curve along which the lens effect is more pronounced. The farther an object is from the critical curve, the weaker its image appears to us - and the image is replicated in two or more copies. Multiple images occur on opposite sides of the criti- cal curve. This is not the case with Earendel, which not only fits well into the Sunrise Arc, but is also likely to be found in the center of the crit- ical curve path, since its image is not doubled. At most, it deviates from the critical curve by 0.1” and, there-