In 2005, Gaensler was reported to have solved the mystery of why some supernova explosions form magnetars while others form ordinary pulsars. Later that year, he and his colleagues observed one of the brightest explosions ever observed in the history of astronomy, resulting from a sudden pulse of gamma rays from the magnetar SGR 1806-20. In 2005, he reported puzzling new observations of the Large Magellanic Cloud, showing that powerful but unknown forces were at work in maintaining this galaxy's magnetic field.