Free Astronomy Magazine November-December 2023

NOVEMBER-DECEMBER 2023 the true nature of this star, known as HD 45166, beyond the fact that it is rich in helium, somewhat more massive than our Sun, and part of a binary system. “This star became a bit of an obses- sion of mine,” said Tomer Shenar, an astronomer at the University of Am- sterdam and lead author of a study published in the journal Science . Having studied similar helium-rich stars before, Shenar was intrigued by the unusual characteristics of HD 45166, which has some of the char- acteristics of a Wolf-Rayet star, but with a unique spectral signature. He suspected that magnetic fields could explain these perplexing character- istics. “I remember having a Eureka moment while reading the litera- ture: ‘What if the star is mag- netic?’,” he said. Shenar, Chené, and their collabora- tors set out to test this hypothesis by taking new spectroscopic observa- tions of this star system with the CFHT. These observations revealed that this star has a phenomenally powerful magnetic field, about 43,000 gauss, the most powerful magnetic field ever found in a mas- sive star. By also studying its interac- tions with its companion star, the T his artist’s impression shows a highly unusual star that is destined to become one of the most magnetic objects in the Universe: a variant of a neutron star known as a magnetar. This finding marks the discovery of a new type of astro- nomical object — a massive magnetic helium star — and sheds light on the origin of magnetars. In a few million years, HD 45166 will explode as a very bright, but not particularly energetic, supernova. During this explosion, its core will contract, trapping and concentrating the star’s already daunting magnetic field lines. The result will be a neutron star with a mag- netic field far greater than its progenitor. [NOIRLab/AURA/NSF/P. Marenfeld/M. Zamani]