Magnetars are the strongest magnets in the universe. These super-compact extinct stars with ultra-strong magnetic fields can be found all over our Milky Way galaxy, but astronomers aren’t exactly sure how they form. Now researchers, using several telescopes around the world, including facilities at the European Southern Observatory (ESO), have discovered a living star that is likely to become a magnetar. The discovery of this new star type, a heavy magnetic helium star, sheds light on the origin of so-called magnetars.
Although the star has been observed for over a hundred years, the enigmatic nature of HD 45166 was not easily explained by conventional models and little more was known about it than that it is part of a binary star [1], contains a lot of helium and is several times heavier than our sun. “This star became a bit of an obsession for me,” said Tomer Shenar, an astronomer at the University of Amsterdam and lead author of a research paper on the object published today in Science. “Tomer and I call HD 45166 the ‘zombie star’,” says co-author and ESO astronomer Julia Bodensteiner, who works in Germany. “That’s not just because this star is so unique, but also because I jokingly commented that it turns Tomer into a zombie himself.”
Shenar, who had previously studied similar helium-rich stars, thought magnetic fields could solve the issue. Indeed, magnetic fields are known to influence the behavior of stars and could explain why current models failed to characterize HD 45166, located about 3,000 light-years away in the constellation Monoceros (the Unicorn). “I remember when I went through the existing literature, a light bulb went on: ‘What if the star is magnetic?'” says Shenar, who currently works at the Center for Astrobiology in Madrid, Spain.
Shenar and his team set out to investigate the star using various facilities around the world. The most important observations were made in February 2022 with an instrument of the Canada-France-Hawaii Telescope that can detect and measure magnetic fields. In addition, the team also made use of important archival data collected with the Fiber-fed Extended Range Optical Spectrograph (FEROS) at ESO’s La Silla Observatory in Chile. Once the observations came in, Shenar asked co-author Gregg Wade, an expert on magnetic fields in stars at the Royal Military College of Canada, to study the data. Wade’s answer confirmed Shenar’s premonition: “Well, whatever this thing is—it sure is magnetic.”
Shenar’s team found that HD 45166 has an incredibly strong magnetic field of 43,000 gauss, making it the most magnetic massive star ever seen [2]. “The entire surface of the helium star is as magnetic as the strongest man-made magnets,” explains co-author Pablo Marchant, an astronomer at the Institute of Astronomy at KU Leuven in Belgium. This observation marks the discovery of the first ever heavy magnetic helium star. “It’s great to discover a new type of astronomical object,” says Shenar, “especially if it’s been right in front of us all along.” In addition, the object provides clues to the origin of magnetars — compact, extinct stars laced with magnetic fields at least a billion times stronger than HD 45166. The team’s calculations indicate that this star will end up as a magnetar. As it collapses under its own gravity, its magnetic field will strengthen, eventually transforming HD 45166 into an extremely dense core with a magnetic field of about 100 trillion gauss [3] – the most powerful type of magnet in the universe.
Shenar and his team also found that HD 45166 has a smaller mass than previously reported, about twice the mass of the Sun, and that the pair of stars orbit each other at much greater distances than previously believed. In addition, their research indicates that HD 45166 was formed from the merger of two smaller helium-rich stars. “Our findings provide a completely new picture of HD 45166,” Bodensteiner notes.
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[1] Although HD 45166 is a binary star, in this text HD 45166 refers to the helium-rich star, not both.
[2] The magnetic field of 43,000 gauss is the strongest ever measured in a star that exceeds the Chandrasekhar mass limit: the critical limit above which stars can collapse into neutron stars (a magnetar is a type of neutron star).
[3] A trillion is a 1 with twelve zeros.
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The European Southern Observatory (ESO) enables scientists from all over the world to discover the secrets of the universe for the benefit of all. We design, build and operate world-class observatories used by astronomers to answer exciting questions and spread the fascination for astronomy, and promote international collaboration in astronomy. Founded in 1962 as an intergovernmental organisation, ESO is now supported by 16 Member States (Austria, Austria, Belgium, Denmark, Finland, France, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, the Czech Republic, the United Kingdom, Sweden and Switzerland) and by the host country Chile, with Australia as a strategic partner. ESO’s headquarters and its visitor center and planetarium, the ESO Supernova, are located near Munich in Germany, but our telescopes are located in the Chilean Atacama Desert – a beautiful place with unique conditions for celestial observations. ESO operates three observing sites: La Silla, Paranal and Chajnantor. Paranal houses ESO’s Very Large Telescope and Very Large Telescope Interferometer, as well as survey telescopes such as VISTA. ESO will also host and operate the Cherenkov Telescope Array South at Paranal – the world’s largest and most sensitive gamma-ray observatory. Together with international partners, ESO operates APEX and ALMA on Chajnantor, two facilities that observe the sky in the millimeter and submillimetre region. On Cerro Armazones, near Paranal, we are building ‘the largest eye in the world’ – ESO’s Extremely Large Telescope. From our offices in Santiago, Chile, we support our activities in the host country and work with Chilean partners and Chilean society.
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2023-08-17 18:11:38
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