Illustration showing a source within a galaxy emitting the fast radio burst (FRB) 181112. The radio burst travelled from the host galaxy to reach the Earth and was detected by the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope in 2018. Follow-up observations with European Southern Observatory's (ESO's) Very Large Telescope (VLT) revealed that the radio pulses have passed through the halo of a massive galaxy on their way toward Earth. This finding allowed astronomers to analyse the radio signal for clues about the nature of the halo gas.