The discovery of a new type of star could provide astronomers with clues to the mysterious origin of magnetars
Magnetars are the strongest magnets in the universe; the super-dense dead stars with ultra-strong magnetic fields can be found all over our galaxy but astronomers don’t know exactly how they form.
Now, using multiple telescopes around the world, including European Southern Observatory (ESO) facilities, researchers have uncovered a living star that is likely to become a magnetar.
This finding marks the discovery of a new type of astronomical object – massive magnetic helium stars – and sheds light on the origin of magnetars.
Despite having been observed for over 100 years, the enigmatic nature of the star HD 45166 could not be easily explained by conventional models, and little was known about it beyond the fact that it is one of a pair of stars, is rich in helium and is a few times more massive than our sun.
Tomer Shenar, the lead author of a study on this object and an astronomer at the University of Amsterdam, said: “This star became a bit of an obsession of mine,”
Co-author and ESO astronomer Julia Bodensteiner, based in Germany, said: “Tomer and I refer to HD 45166 as the ‘zombie star’.
“This is not only because this star is so unique, but also because I jokingly said that it turns Tomer into a zombie.”
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‘What if the star is magnetic?’
Having studied similar helium-rich stars before, Shenar thought magnetic fields could crack the case.
Indeed, magnetic fields are known to influence the behaviour of stars and could explain why traditional models failed to describe HD 45166, which is located about 3,000 light-years away in the constellation Monoceros.
Shenar, who is currently based at the Centre for Astrobiology in Madrid, Spain, said: “I remember having a Eureka moment while reading the literature: ‘What if the star is magnetic?’”
Shenar and his team set out to study the star using multiple facilities around the globe.
The main observations were conducted in February 2022 using an instrument on the Canada-France-Hawaii Telescope that can detect and measure magnetic fields.
The team also relied on key archive data taken with the Fibre-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 that the star “is definitely magnetic”.
Shenar’s team had found that the star has an incredibly strong magnetic field, of 43,000 gauss, making HD 45166 the most magnetic massive star found to date.
Co-author Pablo Marchant, an astronomer at KU Leuven’s Institute of Astronomy in Belgium, said: “The entire surface of the helium star has a magnetic field almost 100,000 times stronger than Earth’s.”
This observation marks the discovery of the very first massive magnetic helium star.
Shenar said: “It is exciting to uncover a new type of astronomical object, 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 calculations suggest that this star will end its life as a magnetar.
As it collapses 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 distance than believed before.
Furthermore, their research indicates that HD 45166 formed through the merger of two smaller helium-rich stars.
Bodensteiner concluded: “Our findings completely reshape our understanding of HD 45166.”
The study is published in Science.
Image: This artist’s 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. Astronomers believe that this star will end its life as a magnetar, a compact and highly magnetic stellar corpse. As HD 45166 collapses 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. HD 45166 is part of a binary system. In the background, we get a glimpse of HD 45166’s companion, a normal blue star that has been found to orbit at a far larger distance than previously reported. Credit: ESO/ L Calçada.
