Pinpointing a single fast radio burst: Fast radio bursts (FRBs) are flashes of radio emission from distant astronomical sources. Two FRBs are known to have repeated, but most last just a few milliseconds and are never seen again. Most telescopes that are sensitive to single FRBs have poor angular resolutions, so the FRB host galaxies remain unknown. Bannister et al. used a dedicated observing mode on a radio interferometer to detect and localize the nonrepeating FRB 180924, then followed up with optical telescope observations (see the Perspective by Petroff). They found that the FRB came from a medium-sized galaxy at a cosmological distance. Localizing FRBs will help determine their causes and allow them to be used as cosmological probes. Science , this issue p. 565 ; see also p. 546

Probing a galaxy halo with a radio burst: Fast radio bursts (FRBs) are millisecond flashes of radio emission from distant galaxies. It has only recently become possible to locate single bursts precisely enough to determine the host galaxy. Prochaska et al. have observed and localized a FRB using a radio interferometer. The line of sight to the host galaxy coincidentally passes through the outskirts of a closer foreground galaxy. By analyzing the propagation of the FRB, the authors put constraints on the density and magnetization of gas in the outskirts of the foreground galaxy. The technique provides complementary information to existing methods using background quasars. Science , this issue p. 231