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The neutron was discovered by British physicist James Chadwick in 1932 itself. Following him, Werner Heisenberg, one of the discoverers of quantum mechanics, proposed and developed the modern atomic model of atoms composed of neutrons and protons. In 1934, it was the turn of Italian physicist Enrico Fermi, who furthered our understanding of the nucleus by proposing a theory of beta radioactivity taking into account the existence of the particle, proposed in 1930 by Wolfgang Pauli, another great name in quantum theory. extended. The law of conservation of energy in some nuclear reactions.
According to Fermi’s principle, when a neutron decays into a proton by beta radioactivity, not only an electron is emitted, but also a neutrino, more precisely its antiparticle. We can also envisage an opposite process in which a proton combines with an electron to give a neutron and a neutrino.
The year 1934 is also the year American astrophysicists Fritz Zwicky and Walter Baade understood that Type II supernovae are massive explosions of stars that gravitationally collapse using the phenomenon described by the Fermi theory to form neutron stars.
What is a neutron star? What is the difference between these stars and our Sun? CEA astrophysicist Roland Lehauc explains to us that neutron stars, unlike our Sun, emit very little visible light. Furthermore, neutron stars are much smaller in size than the Sun: a neutron star has a diameter of between 10 and 15 km, while the Sun has a diameter of 1.4 million km. They are also compact objects that contain a large amount of material in a very small amount of space. The study of these stars makes it possible to test nuclear physics theories on a different scale. A video co-produced with L’Esprit Sorcière. © CEA Research
neutron stars created by supernovas
In 1939, Robert Oppenheimer would theoretically study this hypothesis more closely with his Russian-born Canadian doctoral student George Volkoff. The two men would then give the first detailed theoretical description of neutron star formation. But it was not until 1967 that Jocelyn Bell made her discovery as a pulsar.
Later, a new chapter in the neutron star saga would open with the discovery of magnetars, neutron stars with magnetic fields of very high intensity, already exceeding the exotic field of classical neutron stars.
Since then, astrophysicists have been trying to understand the origin of the magnetar and researchers from several telescopes around the world, including the European Southern Observatory (ESO), have opened up a fascinating path. As stated in a publication ScienceAstrophysicists have discovered a massive helium star that is already endowed with a strong magnetic field, a magnetic field that can only be enhanced by the collapse of the star’s heart during a supernova explosion.
The explosion of very massive stars in gravitational supernovae enriches the interstellar medium with chemical elements synthesized by nuclear fusion, while neutron stars or black holes are formed by the collapse of the star’s core. The transition between core collapse and stellar mantle ejection is a challenge to the theoretical understanding of supernovae. A hydraulic experiment designed and carried out at the CEA made it possible to reproduce by analogy one of the hydrodynamic instability events that facilitated the eruption. This experimental approach is complementary to numerical simulations. Check out this animation experience. This animated film was produced and co-financed by CEA and ERC, and directed by Studio Anime. Scientific and Technological Design: T. Foglizzo, J. Guillet, G. Durand (CEA). © CEA Research
magnetic field of 100,000 billion gauss
There is in fact a law of conservation of magnetic flux (derived from Maxwell’s equations, see Feynman’s course on the subject), which implies that the product of the surface of the star and the intensity of the magnetic field along the field lines crossing this surface is continuous. If the surface of the star is reduced by the collapse, the magnetic field emanating from this surface will become more intense.
An ESO statement associated with the discovery said it was nothing less than the discovery of a new type of celestial object – giant magnetized helium stars – which appears to have occurred. Amazingly, we’ve known and seen this first example for over a century, right in front of our noses, but we’ve yet to discover the nature of HD 45166, a star in the Unicorn constellation about 3,000 light-years away from the Solar System. Couldn’t understand. ,
It was Tomar Schenar, an astronomer at the University of Amsterdam in the Netherlands, who first began to think that the sometimes puzzling behavior of this star twice as massive as the Sun and part of a double might be explained if it There was a much stronger magnetic field than previously thought. With colleagues such as Greg Wade, an expert on the magnetic fields of stars Royal Military College of CanadaHe wanted to find out for sure, using measurements provided by the Canada-France-Hawaii Telescope and archival data obtained from the FERROS instrument. (Extended Range Optical Spectrograph with Fiber) At ESO’s La Silla Observatory in Chile.
It was found that HD 45166 is the most magnetic giant star ever discovered with an average magnetic field of 43,000 Gauss. For comparison, Earth’s magnetic field has an average value of about 0.5 gauss.
Calculations show that in a neutron star collapse, this magnetic field intensity would increase to 100,000 billion gauss, which is about the order of magnitude of a magnetar’s field.
Using multiple telescopes around the world, including facilities at the European Southern Observatory (ESO), researchers have discovered a living star that has the potential to become a magnetar, a super-magnetized dead star. This video summarizes the search. To get a fairly accurate French translation, click on the white rectangle at the bottom right. Then the English subtitles should appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Select “French”.
Wolf-Rayet type helium core
HD 45166 behaves like the mostly helium core of a more massive star whose mantle has been torn apart. But there are many arguments against this explanation. This star appears to have initially been the result of a complex fusion evolution of two more massive standard stars. It can be shown that we then obtain the observed Wolf–Rayet type star and that this explains the formation of its intense magnetic field. Typically, a WR star has several tens of solar masses, and only normal stars with at least 8 to 10 solar masses can become neutron stars, but the evolution and stellar composition for this star are different and non-standard. Helium of only 2 solar masses.