Astrophysics: A neutron star born from supernova ash


A neutron star was indeed born from the remnants of supernova 1987A, the most studied in the history of astronomy and the only one visible to the naked eye in the last 400 years. This celestial body, defined as “degenerate” (composed mainly of neutrons held together by the force of gravity), is formed after the gravitational collapse of a massive star (very hot and large, also called blue because of its color), whose peak moment is a supernova explosion. It thus represents one of the possible final stages of stellar evolution. Paradoxically, when a star becomes very large, it does not “get stronger”, but weakens, becoming more fragile, thus hastening its end.

This was demonstrated by scientists from Stockholm University and the Royal Observatory in the United Kingdom, who published an article in the journal Science. A research team led by Claes Fransson collaborated with international astronomers and experts to observe supernova 1987A using the James Webb Space Telescope (JWST).. Although the star has been the subject of advanced observation for more than three decades, conclusive proof of the existence of a neutron star has not yet been found. Some circumstantial evidence, on the other hand, suggested the hypothesis that a black hole had been created. Experts explain that supernovae are stars with a mass eight times that of the Sun and represent the origin of various chemical elements. Their core can turn into a neutron star or a black hole after the explosion.

Supernova 1987A, located in a nearby dwarf galaxy, was the closest and brightest supernova seen in four centuries. The presence of the expanding debris hid the compact object at the center of the explosion, making it difficult to detect a black hole or neutron star. The research team observed the remnants of the star at infrared wavelengths with JWST using spectroscopy to examine the composition and motions of the gas. Experts have identified emission lines of highly ionized argon and sulfur gas located near where the star exploded. Gas composition and ionization can only be explained if there is a light source of ultraviolet and X-ray radiation from a neutron star. This work therefore allowed us to rule out the presence of a black hole and confirmed that supernova 1987A did indeed form a neutron star.

Still mindful of the progress in understanding the universe, theoretical physicists instead hypothesized the possibility of a “Matryoshka” star, a celestial body that has another smaller star inside, but of the same type. This fascinating result is a “solution” to the field equations of general relativity, a mathematical treatment obtained by Daniel Jampolski and Luciano Rezzolla of Goethe University in Frankfurt, who published their theory in Classical and quantum gravity. Specifically, both authors talk about the gravastar, a star model that presents itself as an alternative to the idea of ​​black holes. These gravastars were hypothesized to be the result of solutions to Einstein’s field equations by Pawel Mazur and Emil Mottola. Unlike black holes, gravastars have several advantages in terms of theoretical astrophysics. On the one hand, they are almost as compact as black holes, and they also exhibit gravity on their surface that is essentially as strong as a black hole, so they resemble a full-fledged black hole. On the other hand, gravastars do not – again theoretically – have an event horizon, that is, they have not exceeded – by density – a threshold value for which no information can be sent out from then and their core is not generated by a singularity (i.e. a point that attracts everything without anything discharged out as in black holes). Instead, again in theory, the center of gravastars is made up of exotic – dark – energy that exerts a negative pressure on the enormous gravitational force that compresses the star. The surface of gravastars is a very thin crust of ordinary matter, the thickness of which is close to zero. Now in a new formulation of this theory developed by Daniel Jampolski and Luciano Rezzola, the existence of a gravastar inside another gravastar would be possible, the two scientists gave this hypothetical celestial object the name “nestar”.


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