Une image composite formée de photos de l'observatoire de Las Cumbres et du télescope spatial Hubble montrant la supernova à capture d'électrons 2018zd (le cercle, en haut à droite) et sa galaxie hôte NGC 2146 (vers la gauche). © Nasa/STScI/J. DePasquale ; Observatoire de Las Cumbres

We would have finally noticed a strange supernova with electron capture

After the supernovae of antimatter, here are the electron-capturing supernovae. The concept is about 40 years old, but a series of powerful observations seem to show that the universe was aware of the speculations of astrophysicists and that the SN 2018zd supernova is indeed an example of this strange phenomenon that probably also describes the famous supernova of 1054.

international team ofastrophysicists Comes to announce that the first convincing example of the type Supernova Alien has been predicted in theory for nearly 40 years, particularly by numerical simulation I know, it was finally discovered. These researchers have published an article in natural astronomy (Copy available at arXiv) around the supernova SN 2018zd that occurred in galaxy NGC 2146, about 31 millionlight years from Milky Way.

The Photons From SN 2018zd fell first in the net Las Cumbres Observatory But since the supernova it has had several anomaly which did not allow it to fit within the framework of the two main types of supernovae now well known, astrophysicists delved into the astronomical archives of the noospheres that preserved the memory of galactic observations NGC 2146, do it with telescope Hubble. Pictures of this spiral galaxy, located in constellation from giraffe, revealed thatstar SN 2018zd’s predecessor was a massive star that is said to be in the super asymptotic branch of giants (Super convergent giant branch or Sagb in English).

Nuclear astrophysics, the key to supernovae

Let us remember that at the beginning of the 1930s, astrophysicists Walter Bade and Fritz Zwicky realized that it was necessary to introduce a new category in astronomy. nove, these bright transiting stars appear only once in the sky and then disappear forever. The name they propose will bring fortune: Supernova. En compagnie de Rudolph Minkowski, astronomer And the nephew of the famous mathematician, Hermann Minkowski, Buddy realizes that these supernovae can also be separated into two types, depending on the spectral lines and characteristics of light curves whose changes vary over several weeks in particular. Other sections will be added but this work is the origin of modern taxonomy with SN II and SN Ia.

Also in the 1930s, Walter Bade and Fritz Zwicky, very soon after Chadwick discovered neutron In 1932, some supernovae are massive explosions. accompanyCollapse The stars that will become neutron stars. In 1938, Robert Oppenheimer He uses, with his student Volkov, the results of Richard Tolman regarding the fluid fields in general relativityand makes the first real calculations of the concept of neutron stars. As early as 1939, these two researchers presented them as atomic nuclei the size of a star. Together with fellow student Hartland Snyder, Oppenheimer will study what happens to such objects when they collapse gravitationally, laying the foundation for a theory black holes.

Neutron star production usually occurs with a star of at least 10 . masses Solar cells, whose iron-containing core is no longer a site for thermonuclear reactions, producing enoughenergy in the form of photons so that radiation pressure The resulting may conflict gravity from the star. Then it collapses, resulting in an SN II supernova. During this breakdown, the stress becomes like this Electrons About iron cores can combine with protons to give neutrons and neutrino flux According to the reverse reaction of the decay reaction by Radioactivity beta.

In the case of SN Ia, things are quite different. It all starts with a star less than 8 solar masses that evolves with a loss of mass and ends up having an inert core containing nucleiOxygen Based on Carbon Basically. Thermonuclear reactions also stopped at this point and as long as the mass stopped white dwarf Not beyond famous Chandrasekhar حد limit (about 1.4 solar masses), the star does not collapse under its influence gravity Because there is a Gas decompose of relativ electrons as we say in language Quantum physics. A white dwarf will explode with a thermonuclear explosion if received from a companion star of ل Thing Across accumulation So much so that its mass exceeds that of Chandrasekhar.

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Relative electron gas absorbed by the nuclei

An attentive reader will note that until now there has been no doubt about the fate of stars with masses between 8 and 10 solar masses. To specifically explain the fate that awaits them, the theory of electronic supernovae was formulated in the early 1980s by Kenichi Nomoto de University of Tokyo, then by other nuclear astrophysicists.

For these stars, they also evolve into a white dwarf but their core begins to contain بال neon And you magnesium instead of carbon. There comes a time when these cores capture decaying electron gas even though the star was not massive enough to produce the thermonuclear reactions leading to iron cores.

When the electron gas disappears, the degenerative pressure Also, which leads to the release of energy and the collapse of gravity giving a new type of supernova, the electron supernova, but also with a core of neutrons left over from the explosion.

The fact that the generator star of SN 2018zd was indeed Sagb, and therefore with sufficient mass, that chemical composition anomalies were detected and that the supernova did not produce many radioactive elements, argues for other properties that make SN 2018zd a very strong candidate for the electronic supernova title.

If this is the case, this gives us more confidence in a hypothesis that has been proposed in the case of a mythical supernova, that of 1054 and which we still observe to the rest of the day in addition to the resulting neutron star which is also a neutron star. pulsar. In fact, some astrophysicists let it be known that, according to the data of that time, a supernova Crab Nebula It was relatively bright compared to SN II models that produce a neutron star. They concluded that his brightness It may have been artificially enhanced by supernova collisions with matter rejected by the original star, as shown in the case of SN 2018zd, and as predicted by electronic supernova models predicting significant mass losses before the star exploded.

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