This star could become one of the strongest magnets in the universe

18 Aug 2023

Artist's impression of HD 45166. Image: ESO/L. Calçada

Astronomers have solved a mystery surrounding a massive magnetic helium star around 3,000 light years away that may provide clues to the origin of magnetars.

The more we study the universe, the more bizarre and mysterious objects we find. The latest astronomical object discovered by scientists is the most magnetic massive star found to date.

Known as HD 45166, the star is one of a pair in a binary system and is situated about 3,000 light years away in the Monoceros constellation. It has baffled astronomers for more than 100 years because its behaviour could not be explained by conventional models.

Rich in helium and a few times more massive than our Sun, HD 45166 has been somewhat of an obsession for Tomer Shenar, an astronomer at the University of Amsterdam and lead author of the study published in Science yesterday (17 August).

“Tomer and I refer to HD 45166 as the ‘zombie star’,” said co-author Julia Bodensteiner, an astronomer based at the European Southern Observatory in Germany. “This is not only because this star is so unique, but also because I jokingly said that it turns Tomer into a zombie.”

While Shenar has studied similar helium-rich stars before, he wasn’t sure why conventional models could not explain the behaviour of HD 45166. But then he stumbled upon an idea.

“I remember having a Eureka moment while reading the literature: ‘What if the star is magnetic?’,” said Shenar, currently based at the Centre for Astrobiology in Madrid.

He then began an investigation using observations from 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 Fiber-fed Extended Range Optical Spectrograph (FEROS) at the European Southern Observatory’s (ESO) La Silla Observatory in Chile.

After the observations were analysed by co-author Gregg Wade, an expert on magnetic fields in stars at the Royal Military College of Canada, it was confirmed that HD 45166 has an “incredibly strong” magnetic field – the most magnetic massive star found to date.

“The entire surface of the helium star has a magnetic field almost 100,000 times stronger than Earth’s,” explained co-author Pablo Marchant, an astronomer at KU Leuven’s Institute of Astronomy in Belgium.

The team believes the study can help astronomers better understand the origin and evolution of magnetars, which are super-dense dead stars with ultra-strong magnetic fields that are the strongest magnets in the universe.

In fact, the study found that HD 45166 is likely on its way to becoming one – and a very powerful one. “It is exciting to uncover a new type of astronomical object,” added Shenar, ”especially when it’s been hiding in plain sight all along.”

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Vish Gain is a journalist with Silicon Republic