Strongly Magnetic Wolf-Rayet Star Likely to Birth Magnetar

Observations and stellar evolution models of a hot, helium-rich Wolf-Rayet star indicate that it will produce a magnetar when it explodes as a supernova, according to a new study. The findings provide new insights into how magnetars – the most magnetic objects in the Universe – are formed. A magnetar is a type of neutron star with an extremely powerful magnetic field. Neutron stars form in supernovae that occur when the core of a massive star collapses. However, the origins of magnetars remain unclear. One proposal is that amplification of a magnetic field in the massive core of the parent star could produce a magnetar during a supernova explosion. However, such magnetic fields have not been observed in evolved stars that are massive enough to form neutron stars when they explode. Tomar Shenar and colleagues report observations of HD 45166, a binary system that comprises a main sequence star with a hot Wolf-Rayet star companion. Wolf-Rayet stars are the exposed helium core of a massive star that has lost its outer layers of hydrogen. Using new spectropolarimetric observations of HD45166 obtained by the Canada-France-Hawaii Telescope and archival spectra from other instruments, Shenar et al. found that the Wolf-Rayet component has a mass of 2 solar masses and a high magnetic field of 43 kilogauss. The authors ran stellar evolution models incorporating these data, which indicate that the Wolf-Rayet component will eventually collapse into a neutron star. They calculate that magnetic flux conservation during core collapse would increase the strength of the magnetic field to within the range of what is observed for magnetars. "Our observations and stellar-evolution models therefore indicate that the Wolf-Rayet component could be an immediate progenitor of a magnetar," write the authors.