Free Astronomy Magazine September-October 2020

30 SEPTEMBER-OCTOBER 2020 SPACE CHRONICLES by ESO ALMA sees most distant Milky Way look-alike A stronomers using the Ata- cama Large Millimeter/sub- millimeter Array (ALMA), in which the European Southern Ob- servatory (ESO) is a partner, have re- vealed an extremely distant and therefore very young galaxy that looks surprisingly like our Milky Way. The galaxy is so far away its light has taken more than 12 billion years to reach us: we see it as it was when the Universe was just 1.8 bil- lion years old. It is also surprisingly unchaotic, contradicting theories that all galaxies in the early Universe were turbulent and unstable. This unexpected discovery chal- lenges our understanding of how galaxies form, giving new insights into the past of our Universe. “This result represents a break- through in the field of galaxy forma- tion, showing that the structures that we observe in nearby spiral galaxies and in our Milky Way were already in place 12 billion years ago,” says Francesca Rizzo, PhD stu- dent from the Max Planck Institute for Astrophysics in Germany, who led the research published in Nature . While the galaxy the astronomers studied, called SPT0418-47, doesn’t appear to have spiral arms, it has at least two features typical of our A stronomers using ALMA, in which the ESO is a partner, have revealed an extremely distant galaxy that looks surprisingly like our Milky Way. The galaxy, SPT0418-47, is gravitationally lensed by a nearby galaxy, appearing in the sky as a near-perfect ring of light. [ALMA (ESO/NAOJ/NRAO), Rizzo et al.] Milky Way: a rotating disc and a bulge, the large group of stars packed tightly around the galactic centre. This is the first time a bulge has been seen this early in the history of the Universe, making SPT0418-47 the most distant Milky Way look-alike. “The big surprise was to find that this galaxy is actually quite similar to nearby galaxies, contrary to all ex- pectations from the models and pre- vious, less detailed, observations,” says co-author Filippo Fraternali, from the Kapteyn Astronomical In- stitute, University of Groningen in