Free Astronomy Magazine September-October 2023

47 SEPTEMBER-OCTOBER 2023 ASTRO PUBLISHING 2022 using an instrument on the Canada-France-Hawaii Telescope that can detect and measure mag- netic fields. The team also relied on key archive data taken with the Fiber-fed Extended Range Optical Spectrograph (FEROS) at ESO’s La Silla Observatory in Chile. Once the observations were in, Shenar asked co-author Gregg Wade, an expert on magnetic fields in stars at the Royal Military College of Canada, to examine the data. Wade’s response confirmed Shenar’s hunch: “Well my friend, whatever this thing is — it is definitely magnetic.” Shenar’s team had found that the star has an in- credibly strong magnetic field, of 43,000 gauss, making HD 45166 the most magnetic massive star found to date. “The entire surface of the helium star has a magnetic field al- most 100,000 times stronger than Earth’s,” explains co-author Pablo Marchant, an astronomer at KU Leuven’s Institute of Astronomy in Belgium. This observation marks the discov- ery of the very first massive mag- netic helium star. “It is exciting to uncover a new type of astronomical object, — says Shenar, — especially when it’s been hiding in plain sight all along.” Moreover, it provides clues to the origin of magnetars, compact dead stars laced with magnetic fields at least a billion times stronger than the one in HD 45166. The team’s cal- culations suggest that this star will end its life as a magnetar. As it col- lapses under its own gravity, its magnetic field will strengthen, and the star will eventually become a very compact core with a magnetic field of around 100 trillion gauss — the most powerful type of magnet in the Universe. Shenar and his team also found that HD 45166 has a mass smaller than previously reported, around twice the mass of the Sun, and that its stellar pair orbits at a far larger dis- tance than believed before. Further- more, their research indicates that HD 45166 formed through the merger of two smaller helium-rich stars. “Our findings completely re- shape our understanding of HD 45166,” concludes Bodensteiner. ! T his artist impression shows HD 45166, a massive star recently discovered to have a powerful magnetic field of 43 000 gauss, the strongest magnetic field ever found in a massive star. Intense winds of particles blowing away from the star are trapped by this magnetic field, enshrouding the star in a gaseous shell as illustrated here. [ESO/L. Calçada]