A new type of star offers clues to the origin of magnetars

Everywhere in our galaxy one finds dead stars with a very high density and extremely strong magnetic fields: the magnetars, the strongest magnets in the cosmos. This is a type of neutron star that is formed when massive stars collapse and explode in a supernova. However, the origin of the magnetar type is unclear.

Now a team of researchers using multiple telescopes has discovered a living star that is likely to become a magnetar. This finding was published in Sciencemarks the discovery of a new type of astronomical object: massive magnetic helium starsin addition to shedding light on the mysterious origin of magnetars.

The first massive magnetic helium star has been discovered: it is rich in helium and part of the binary star system HD 45166

Despite being observed for more than 100 years, conventional models have failed to explain the enigmatic nature of either of the two stars that make up the galaxy. binary HD 45166, particularly the one rich in helium and a few times more massive than our sun. Little else was known about him, the protagonist of the new study, who belongs to a group of hot and evolved stars called Wolf-Rayet.

“This star almost became an obsession”, It says Tom ShenarLead author of a study and astronomer at the University of Amsterdam (Netherlands).

“Tomer and I refer to HD 45166 (it’s the helium-rich star in this context, not the two in the binary) as Zombie Star, That’s not only because it’s so unique, but because I jokingly said it turns Tomer into a zombie,” says co-author and astronomer Julia Bodensteiner the European Southern Observatory (ESO).

Having previously studied similar helium-rich stars, Shenar believed that the magnetic fields You could solve the case. In fact, these fields are known to affect stellar behavior and may explain why conventional models have failed to describe the behavior of HD 45166, which resides there about 3000 light years away, in the constellation Monoceros.

Examination after the eureka moment

“I remember having an aha moment reading the literature about it: What if the star was magnetic?”, says Shenar, who currently works at the Center for Astrobiology (CAB) in Madrid.

Shenar and his team set out to study the star using multiple facilities around the world. The main observations were made in February 2022 with an instrument installed in the Canada France Hawaii Telescope that can detect and measure magnetic fields.

Researchers also drew on key archival data collected with the FEROS (Fiber-fed Extended Range Optical Spectrograph) instrument, located at ESO’s La Silla Observatory in Chile.

After the observations were made, Shenar asked the co-author Gregg Wade, an expert in stellar magnetic fields from the Royal Military College of Canada, to examine the data. Wade’s response confirmed Shenar’s suspicion: “Well my friend, whatever it is, it’s definitely magnetic.”.

The star has an incredibly strong magnetic field of 43,000 gauss, making it the most magnetic and massive star found to date.

Shenar’s team found that the star has an incredibly strong magnetic field of 43,000 gauss, making HD 45166 the most magnetic and massive star found to date.

This value represents the strongest magnetic field ever measured in a star, exceeding the so-called Chandrasekhar mass limitabove which stars, like magnetars, can collapse into neutron stars.

“Across the entire surface of this helium star, there is a magnetic field about 100,000 times stronger than Earth’s.”, explains the co-author, Paul MarchantAstronomer at the Institute for Astronomy at KU Leuven (Belgium).

This observation marks the discovery of the first massive magnetic helium star. “It’s exciting to discover a new type of astronomical object”, says Shenar, “especially if it’s been hiding in plain sight the whole time.”

It’s exciting to discover a new type of astronomical object, especially when it’s been hidden from the public eye all along.”

Tomer Shenar (University of Amsterdam/CAB)

In addition, it offers Clues to the origin of magnetarscompact dead stars associated with magnetic fields at least a billion times stronger than that of HD 45166.

Birth of the magnetar after the death of the star

In fact, 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 increases, and eventually the star becomes a very compact core with a magnetic field of about 100 trillion gauss, the strongest type of magnet in the universe.

It was formed by the merger of two smaller helium-rich stars.

Shenar and his team also discovered that HD 45166 has one smaller mass than previously calculated, about twice as massive as the Sun, and that its pair of stars orbits at a much greater distance than previously thought.

In addition, their investigations suggest that HD 45166 was formed by the merger of two smaller, helium-rich stars. “Our findings completely change our understanding of HD 45166,” Bodensteiner concludes.


Tomer Shenar et al. “A massive helium star with a strong enough magnetic field to form a magnetar.” Science2023

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