Free Astronomy Magazine September-October 2020

31 SEPTEMBER-OCTOBER 2020 SPACE CHRONICLES powerful telescopes are almost im- possible as the galaxies appear small and faint. The team overcame this obstacle by using a nearby galaxy as a powerful magnifying glass — an effect known as gravitational lens- ing — allowing ALMA to see into the distant past in unprecedented detail. In this effect, the gravita- tional pull from the nearby galaxy distorts and bends the light from the distant galaxy, causing it to ap- pear misshapen and magnified. The gravitationally lensed, distant galaxy appears as a near-perfect ring of light around the nearby galaxy, thanks to their almost exact alignment. The research team re- constructed the distant galaxy’s true shape and the motion of its gas from the ALMA data using a new computer modelling technique. “When I first saw the reconstructed image of SPT0418-47 I could not be- lieve it: a treasure chest was open- ing,” says Rizzo. “What we found was quite puz- zling; despite forming stars at a high rate, and therefore being the site of highly energetic processes, SPT0418- 47 is the most well-ordered galaxy disc ever observed in the early Uni- verse,” stated co-author Simona Vegetti, also from the Max Planck In- stitute for Astrophysics. “This result is quite unexpected and has impor- tant implications for how we think galaxies evolve.” The astronomers note, however, that even though SPT0418-47 has a disc and other fea- tures similar to those of spiral galax- ies we see today, they expect it to evolve into a galaxy very different from the Milky Way, and join the class of elliptical galaxies, another type of galaxies that, alongside the spirals, inhabit the Universe today. This unexpected discovery suggests the early Universe may not be as chaotic as once believed and raises many questions on how a well-or- dered galaxy could have formed so soon after the Big Bang. This ALMA finding follows the ear- lier discovery announced in May of a massive rotating disc seen at a sim- ilar distance. SPT0418-47 is seen in finer detail, thanks to the lensing ef- fect, and has a bulge in addition to a disc, making it even more similar to our present-day Milky Way than the one studied previously. Future studies, including with ESO’s Extremely Large Telescope, will seek to uncover how typical these ‘baby’ disc galaxies really are and whether they are commonly less chaotic than predicted, opening up new avenues for astronomers to discover how galaxies evolved. T he galaxy SPT0418-47 is gravita- tionally lensed by a nearby gal- axy, appearing in the sky as a near- perfect ring of light. The research team reconstructed the distant galaxy’s true shape and the motion of its gas (right) from the ALMA data using a new computer modelling technique. The observations indicate that SPT0418-47 is a disc galaxy with a central bulge and the material in it rotates around the centre. Gas mov- ing away from us is shown in red, while gas moving in the direction of the observer is shown in blue. [ALMA (ESO/NAOJ/NRAO), Rizzo et al.] the Netherlands. In the early Uni- verse, young galaxies were still in the process of forming, so re- searchers expected them to be chaotic and lacking the distinct structures typical of more mature galaxies like the Milky Way. Studying distant galaxies like SPT0418-47 is fundamental to our understanding of how galaxies formed and evolved. This galaxy is so far away we see it when the Uni- verse was just 10% of its current age because its light took 12 billion years to reach Earth. By studying it, we are going back to a time when these baby galaxies were just be- ginning to develop. Because these galaxies are so far away, detailed observations with even the most !