Free Astronomy Magazine November-December 2019

49 NOVEMBER-DECEMBER 2019 SPACE CHRONICLES the radio signal for clues about the nature of the halo gas. “The signal from the fast radio burst exposed the nature of the magnetic field around the galaxy and the structure of the halo gas. The study proves a new and transformative technique for exploring the nature of galaxy halos,” said J. Xavier Prochaska, pro- fessor of astronomy and astrophysics at the University of California Santa Cruz and lead author of a paper pre- senting the new findings published today in the journal Science . Astronomers still don’t know what causes fast radio bursts and only re- cently have been able to trace some of these very short, very bright radio signals back to the galaxies in which they originated. “When we overlaid the radio and optical images, we could see straight away that the fast radio burst pierced the halo of this coincident foreground galaxy and, for the first time, we had a direct way of investigating the otherwise invisible matter surrounding this galaxy,” said coauthor Cherie Day, a PhD student at Swinburne University of Technology, Australia. A galactic halo contains both dark and ordinary − or baryonic − matter T his artist’s impression repre- sents the path of the fast radio burst FRB 181112 traveling from a distant host galaxy to reach the Earth. FRB 181112 was pinpointed by the Australian Square Kilometre Array Pathfinder (ASKAP) radio tel- escope. Follow-up observations with ESO’s Very Large Telescope (VLT) revealed that the radio pulses have passed through the halo of a massive galaxy on their way to- ward Earth. This finding allowed astronomers to analyse the radio signal for clues about the nature of the halo gas. [ESO/M. Kornmesser]