Magnets are the strongest magnets in the universe. These extinct, ultra-small stars with super-strong magnetic fields can be found throughout our Milky Way galaxy, but astronomers aren’t quite sure how they formed. Now researchers, using many telescopes around the world, including facilities at the European Southern Observatory (ESO), have discovered a living star with the potential to become a magnetar. The discovery of this new type of star, a heavy helium magnetar, sheds light on the origin of so-called magnetars.
Although the star was observed more than a hundred years ago, HD 45166’s nebulous nature is not easily explained by conventional models and little more is known about it than it is part of a binary star. It contains a lot of helium and is several times heavier than our sun. “This star has become a bit of an obsession for me,” said Tomer Schnar, an astronomer at the University of Amsterdam and lead author of a paper on the object published today in the journal Science. “Tomer and I call HD 45166 a “zombie star,” says co-author and ESO astronomer Julia Bodensteiner, who works in Germany. “This is not only because this star is unique, but also because I jokingly remarked that it turns Tomer into a zombie himself. .”
Schnarr, who has previously studied similar helium-rich stars, thinks magnetic fields could solve the problem. In fact, magnetic fields are known to influence the behavior of stars and could explain why current models fail to describe HD 45166, which is located about 3,000 light-years away in the constellation of Monoceros (the Unicorn). “I remember when I was perusing the existing literature, a flashlight would come on: ‘What if the star is a magnetar? “
Schnarr and his team set out to explore the star using various facilities around the world. The most significant observations were made in February 2022 with the Canada-France-Hawaii Telescope instrument that can detect and measure magnetic fields. In addition, the team also made use of important archival data collected using ESO’s Wide Field Optical Spectrometer (FEROS) at La Silla Observatory in Chile. Once the observations came in, Schnarr asked co-author Greg Wade, an expert on magnetic fields in stars at the Royal Military College of Canada, to study the data. Wade’s answer confirmed Schnar’s obsession: “Well, whatever that 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 massive magnetar ever seen. . “The entire surface of a helium star is magnetic, as is the strongest man-made magnet,” 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 helium-heavy magnetar. “It’s great to discover a new type of astronomical object, especially if it’s been right in front of us all the time,” Schnarr says. In addition, the object provides clues to the origin of magnetars – compact and extinct stars that are bound by 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 turning HD 45166 into a very dense core with a magnetic field of about 100 trillion gauss.  The strongest type of magnet in the universe.
Schnarr and his team also found that HD 45166 has a smaller mass than previously reported, about twice that of the Sun, and that the pairs of stars orbit each other at much greater distances than previously thought. In addition, their research indicates that HD 45166 formed from the merger of two smaller, helium-rich stars. “Our findings provide a completely new picture of HD 45166,” notes Bodensteiner.
Nuts Although HD 45166 is a binary star, HD 45166 in this text refers to the helium-rich star, not both.  The magnetic field of 43,000 gauss is the strongest ever seen in a star beyond the Chandrasekhar mass limit: the critical limit above which stars can collapse into neutron stars (a magnetar is a type of neutron star).  A trillion is 1 with twelve zeros.
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 that astronomers use to answer exciting questions, spread fascination with astronomy, and promote international collaboration in astronomy. Founded in 1962 as an intergovernmental organization, ESO is now supported by 16 member states (Austria, Austria, Belgium, Denmark, Finland, France, Germany, Ireland, Italy, Netherlands, Poland, Portugal, Spain, Czech Republic, United Kingdom Sweden and Switzerland) and host country Chile, with Australia as a strategic partner. ESO’s headquarters, visitor center and planetarium, ESO Supernova, is located near Munich, Germany, but our telescopes are located in the Chilean Atacama Desert – a beautiful place with unique conditions for celestial observations. ESO operates three monitoring 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 in Chajnantor, two facilities that monitor the skies in the millimeter and submillimeter regions. At Cerro Armazones, near Paranal, we’re building “the world’s largest eye” – ESO’s Very Large Telescope. From our offices in Santiago, Chile, we support our activities in the host country and work with Chilean partners and the Chilean community.
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