Free Astronomy Magazine November-December 2023

23 NOVEMBER-DECEMBER 2023 ASTRO PUBLISHING participated in the study. It is not clear how early in the life- time of the Universe, and how quickly, mag- netic fields in galaxies form because so far astronomers have only mapped magnetic fields in galaxies close to us. Now, using ALMA, in which the European Southern Observatory (ESO) is a partner, Geach and his team have discovered a fully formed magnetic field in a distant gal- axy, similar in struc- ture to what is ob- served in nearby gal- axies. The field is about 1000 times weaker than the Earth’s magnetic field, but extends over more than 16,000 light- years. “This discovery gives us new clues as to how galactic-scale magnetic fields are formed,” ex- plains Geach. Observing a fully de- veloped magnetic field this early in the history of the Universe indicates that magnetic fields spanning en- tire galaxies can form rapidly while young galaxies are still growing. The team believes that intense star formation in the early Universe could have played a role in acceler- ating the development of the fields. Moreover, these fields can in turn influence how later genera- tions of stars will form. Co-author and ESO astronomer Rob Ivison says that the discovery opens up “a new window onto the inner workings of galaxies, because the magnetic fields are linked to the material that is forming new stars.” To make this detection, the team T his image shows the orientation of the magnetic field in the dis- tant 9io9 galaxy, seen here when the Universe was only 20% of its cur- rent age — the furthest ever detection of a galaxy’s magnetic field. The observations were done with the Atacama Large Millimeter/submil- limeter Array (ALMA), in which ESO is a partner. Dust grains within 9io9 are somewhat aligned with the galaxy’s mag- netic field, and due to this they emit polarised light, meaning that light waves oscillate along a preferred direction rather than randomly. ALMA detected this polarisation signal, from which as- tronomers could work out the orientation of the magnetic field, shown here as curved lines overlaid on the ALMA image. The polarised light signal emitted by the magneti- cally aligned dust in 9io9 was extremely faint, rep- resenting just one per- cent of the total bright- ness of the galaxy, so as- tronomers used a clever trick of nature to help them obtain this result. The team was helped by the fact that 9io9, al- though very distant from us, had been magnified via a process known as gravitational lensing. This occurs when light from a distant galaxy, in this case 9io9, appears brighter and distorted as it is bent by the gravity of a very large object in the foreground. [ALMA (ESO/NAOJ/ NRAO)/J. Geach et al.] T his infrared image shows the distant galaxy 9io9, seen here as a reddish arc curved around a bright nearby galaxy. This nearby galaxy acts as a gravita- tional lens: its mass curves spacetime around it, bend- ing lightrays coming from 9io9 in the background, hence its distorted shape. This colour view results from combining infrared images taken with ESO’s Visible and Infrared Survey Telescope for Astronomy (VISTA) in Chile and the Canada France Hawaii Tele- scope (CFHT) in the US. [ESO/J. Geach et al.] searched for light emitted by dust grains in a distant galaxy, 9io9. Galaxies are packed full of dust grains and when a magnetic field is present, the grains tend to align and the light they emit becomes polarised. This means that the light waves oscillate along a preferred direction rather than randomly. When ALMA detected and mapped a polarised signal coming from 9io9, the presence of a magnetic field in a very distant galaxy was confirmed for the first time. “No other telescope could have achieved this,” says Geach. The hope is that with this and future observations of distant magnetic fields the mystery of how these fun- damental galactic features form will begin to unravel. !