It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Friday, August 18, 2023
Astronomers find progenitor of magnetic monster
Research team including NOIRLab astronomer identify highly unusual star that may evolve into a magnetar — the most magnetic object in the known Universe
ASSOCIATION OF UNIVERSITIES FOR RESEARCH IN ASTRONOMY (AURA)
IMAGE: THIS ARTIST'S IMPRESSION SHOWS A HIGHLY UNUSUAL STAR THAT IS DESTINED TO BECOME ONE OF THE MOST MAGNETIC OBJECTS IN THE UNIVERSE: A VARIANT OF A NEUTRON STAR KNOWN AS A MAGNETAR. THIS FINDING MARKS THE DISCOVERY OF A NEW TYPE OF ASTRONOMICAL OBJECT — A MASSIVE MAGNETIC HELIUM STAR — AND SHEDS LIGHT ON THE ORIGIN OF MAGNETARS. IN A FEW MILLION YEARS, HD 45166 WILL EXPLODE AS A VERY BRIGHT, BUT NOT PARTICULARLY ENERGETIC, SUPERNOVA. DURING THIS EXPLOSION, ITS CORE WILL CONTRACT, TRAPPING AND CONCENTRATING THE STAR’S ALREADY DAUNTING MAGNETIC FIELD LINES. THE RESULT WILL BE A NEUTRON STAR WITH A MAGNETIC FIELD FAR GREATER THAN ITS PROGENITOR.view more
CREDIT: NOIRLAB/AURA/NSF/P. MARENFELD/M. ZAMANI
Neutron stars, the compact remains of a massive star following a supernova explosion, are the densest matter in the Universe. Some neutron stars, known as magnetars, also claim the record for the strongest magnetic fields of any object. How magnetars, which are a mere 15 kilometers across, form and produce such colossal magnetic fields remains a mystery.
New observations by a team of astronomers, including NSF’s NOIRLab’s André-Nicolas Chené, may shed important light on the origin of these magnetic powerhouses. Using various telescopes around the globe, including the Canada-France-Hawai‘i Telescope (CFHT) on Maunakea [1], the researchers have identified a new type of astronomical object — a massive magnetic helium star (an unusual variant of a Wolf-Rayet star), which may be the precursor of a magnetar.
“For the first time, a strong magnetic field was discovered in a massive helium star,” said Chené. “Our study suggests that this helium star will end its life as a magnetar.”
Despite having been observed for more than a century by astronomers, little was known about the true nature of this star, known as HD 45166, beyond the fact that it is rich in helium, somewhat more massive than our Sun, and part of a binary system.
“This star became a bit of an obsession of mine,” said Tomer Shenar, an astronomer at the University of Amsterdam and lead author of a study published in the journal Science. Having studied similar helium-rich stars before, Shenar was intrigued by the unusual characteristics of HD 45166, which has some of the characteristics of a Wolf-Rayet star, but with a unique spectral signature. He suspected that magnetic fields could explain these perplexing characteristics. "I remember having a Eureka moment while reading the literature: ‘What if the star is magnetic?’,” he said.
Shenar, Chené, and their collaborators set out to test this hypothesis by taking new spectroscopic observations of this star system with the CFHT. These observations revealed that this star has a phenomenally powerful magnetic field, about 43,000 gauss [2], the most powerful magnetic field ever found in a massive star. By also studying its interactions with its companion star, the team were able to make precise estimates of its mass and age.
The researchers speculate that, unlike other helium stars that eventually evolve from a red supergiant, this particular star was likely created by the merger of a pair of intermediate-mass stars.
“This is a very specific scenario, and it raises the question of how many magnetars come from similar systems and how many come from other types of systems,” said Chené.
In a few million years, HD 45166, which is located 3000 light-years away in the constellation Monoceros (the Unicorn), will explode as a very bright, but not particularly energetic, supernova. During this explosion, its core will contract, trapping and concentrating the star’s already daunting magnetic field lines. The result will be a neutron star with a magnetic field of around 100 trillion gauss — the most powerful type of magnet in the Universe.
“We thought that the most likely magnetar candidates would come from the most massive of stars,” said Chené. “What this research shows us is that stars that are much less massive can still become a magnetar, if the conditions are just right.”
More information
[1] The team also relied on key archive data taken with the Fiber-fed Extended Range Optical Spectrograph (FEROS) at ESO’s La Silla Observatory in Chile.
[2] Gauss is a unit of measurement of magnetic induction, also known as magnetic flux density (essentially, a measure of magnetic strength). The Sun’s typical polar magnetic field is 1–2 gauss, while sunspots can achieve a magnetic field strength of around 3000 gauss.
Reference: Shenar, T., Wade, G., Marchat, P., et al. 2023, A massive helium star with a sufficiently strong magnetic field to form a magnetar, Science, DOI 10.1126.
NSF’s NOIRLab, the US center for ground-based optical-infrared astronomy, operates the international Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), Kitt Peak National Observatory (KPNO), Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and Vera C. Rubin Observatory (operated in cooperation with the Department of Energy’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona. The astronomical community is honored to have the opportunity to conduct astronomical research on Iolkam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence that these sites have to the Tohono O'odham Nation, to the Native Hawaiian community, and to the local communities in Chile, respectively
A team of researchers, including NOIRLab astronomer André-Nicolas Chené, has found a highly unusual star that may become one of the most magnetic objects in the Universe: a variant of a neutron star known as a magnetar. This finding marks the discovery of a new type of astronomical object — a massive magnetic helium star — and sheds light on the origin of magnetars. Panel one illustrates the system, known as HD 45166, as it appears today. Panel two illustrates how, in a few million years, HD 45166 will explode as a very bright, but not particularly energetic, supernova. During this explosion, its core will contract, trapping and concentrating the star’s already daunting magnetic field lines. Panel three illustrates the ultimate fate of HD 45166 after its core has collapsed, resulting in a neutron star with a magnetic field of around 100 trillion gauss — the most powerful type of magnet in the Universe.
IMAGE: THIS ARTIST 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.view more
CREDIT: ESO/L. CALÇADA
Magnetars are the strongest magnets in the Universe. These 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 [1], is rich in helium and is a few times more massive than our Sun.
“This star became a bit of an obsession of mine,” says Tomer Shenar, the lead author of a study on this object published today in Science and an astronomer at the University of Amsterdam, the Netherlands. “Tomer and I refer to HD 45166 as the ‘zombie star’,” says co-author and ESO astronomer Julia Bodensteiner, based 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."
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 3000 light-years away in the constellation Monoceros. “I remember having a Eureka moment while reading the literature: ‘What if the star is magnetic?’,” says Shenar, who is currently based at the Centre for Astrobiology in Madrid, Spain.
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 Fiber-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: “Well my friend, whatever this thing is — it 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 [2]. “The entire surface of the helium star has a magnetic field almost 100,000 times stronger than Earth's,” explains co-author Pablo Marchant, an astronomer at KU Leuven’s Institute of Astronomy in Belgium [see edit].
This observation marks the discovery of the very first massive magnetic helium star. “It is exciting to uncover a new type of astronomical object,” says Shenar, ”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 [3] — 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. “Our findings completely reshape our understanding of HD 45166,” concludes Bodensteiner.
Edit [17 August]: the quote by Pablo Marchant was changed since a unit conversion mistake led to the previous version being incorrect.
Notes
[1] While HD 45166 is a binary system, in this text HD 45166 refers to the helium-rich star, not to both stars.
[2] The magnetic field of 43 000 gauss is the strongest magnetic field ever detected in a star that exceeds the Chandrasekhar mass limit, which is the critical limit above which stars may collapse into neutron stars (magnetars are a type of neutron star).
[3] In this text, a billion refers to one followed by nine zeros and a trillion refers to one followed by 12 zeros.
More information
This research was presented in a paper to appear in Science (doi: science.org/doi/10.1126/science.ade3293).
The team is composed of Tomer Shenar (Anton Pannekoek Institute for Astronomy, University of Amsterdam, the Netherlands [API], now at the Centre for Astrobiology, Madrid, Spain), Gregg Wade (Department of Physics and Space Science, Royal Military College of Canada, Canada), Pablo Marchant (Institute of Astronomy, KU Leuven, Belgium [KU Leuven]), Stefano Bagnulo (Armagh Observatory & Planetarium, UK), Julia Bodensteiner (European Southern Observatory, Garching, Germany; KU Leuven), Dominic M. Bowman (KU Leuven), Avishai Gilkis (The School of Physics and Astronomy, Tel Aviv University, Israel), Norbert Langer (Argelander-Institut für Astronomie, Universitӓt Bonn, Germany; Max Planck Institute for Radio Astronomy, Bonn, Germany), André Nicolas-Chené (National Science Foundation’s National Optical-Infrared Astronomy Research Laboratory, Hawai‘i), Lidia Oskinova (Institut für Physik und Astronomie, Universitӓt Potsdam, Germany [Potsdam]), Timothy Van Reeth (KU Leuven), Hugues Sana (KU Leuven), Nicole St-Louis (Département de physique, Université de Montréal, Complexe des sciences, Canada), Alexandre Soares de Oliveira (Institute of Research and Development, Universidade do Vale do Paraíba, São José dos Campos, Brazil), Helge Todt (Potsdam) and Silvia Toonen (API).
The European Southern Observatory (ESO) enables scientists worldwide to discover the secrets of the Universe for the benefit of all. We design, build and operate world-class observatories on the ground — which astronomers use to tackle exciting questions and spread the fascination of astronomy — and promote international collaboration for astronomy. Established as an intergovernmental organisation in 1962, today ESO is supported by 16 Member States (Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom), along with the host state of Chile and with Australia as a Strategic Partner. ESO’s headquarters and its visitor centre and planetarium, the ESO Supernova, are located close to Munich in Germany, while the Chilean Atacama Desert, a marvellous place with unique conditions to observe the sky, hosts our telescopes. ESO operates three observing sites: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its Very Large Telescope Interferometer, as well as survey telescopes such as VISTA. Also at Paranal ESO will host and operate the Cherenkov Telescope Array South, the world’s largest and most sensitive gamma-ray observatory. Together with international partners, ESO operates ALMA on Chajnantor, a facility that observes the skies in the millimetre and submillimetre range. At Cerro Armazones, near Paranal, we are building “the world’s biggest eye on the sky” — ESO’s Extremely Large Telescope. From our offices in Santiago, Chile we support our operations in the country and engage with Chilean partners and society.
AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE (AAAS)
Observations and stellar evolution models of a hot, helium-rich Wolf-Rayet star indicate that it will produce a magnetar when it explodes as a supernova, according to a new study. The findings provide new insights into how magnetars – the most magnetic objects in the Universe – are formed. A magnetar is a type of neutron star with an extremely powerful magnetic field. Neutron stars form in supernovae that occur when the core of a massive star collapses. However, the origins of magnetars remain unclear. One proposal is that amplification of a magnetic field in the massive core of the parent star could produce a magnetar during a supernova explosion. However, such magnetic fields have not been observed in evolved stars that are massive enough to form neutron stars when they explode. Tomar Shenar and colleagues report observations of HD 45166, a binary system that comprises a main sequence star with a hot Wolf-Rayet star companion. Wolf-Rayet stars are the exposed helium core of a massive star that has lost its outer layers of hydrogen. Using new spectropolarimetric observations of HD45166 obtained by the Canada-France-Hawaii Telescope and archival spectra from other instruments, Shenar et al. found that the Wolf-Rayet component has a mass of 2 solar masses and a high magnetic field of 43 kilogauss. The authors ran stellar evolution models incorporating these data, which indicate that the Wolf-Rayet component will eventually collapse into a neutron star. They calculate that magnetic flux conservation during core collapse would increase the strength of the magnetic field to within the range of what is observed for magnetars. “Our observations and stellar-evolution models therefore indicate that the Wolf-Rayet component could be an immediate progenitor of a magnetar,” write the authors.
No comments:
Post a Comment