Lightest neutron star ever observed discovered

The Universe is definitely full of surprises. And some undermine the theories developed by scientists. One of the latest – for those interested in stars – is the characterization of a neutron star located within the remains of the supernova HESS J1731-347 by a team from the University of Tübigen . By exploiting in particular the most recent data from the GAIA satellite of the European Space Agency (ESA), she discovered that the mass of the star is much lower than expected: 0.77 times the mass of the Sun, while it was thought until then that this type of object should be at least 1.1 times heavier than our star!

“An intriguing discovery”

A neutron star is formed from the collapse on itself of a massive star (more than 8 times and up to a few tens of times the mass of the Sun; the most massive stars produce black holes). During this cataclysm, a very luminous explosion occurs: it is the famous supernova. It expels the outer layers of the star; its heart contracts and takes the form of a ball of matter so dense that it is no longer made up of atoms, but only of neutrons. More than 3,000 of these so-called “neutron” stars have been identified, whose properties and formation process are still very mysterious today. Any information that deviates from the current models is therefore essential to refine and correct them, and this publication in Nature Astronomy is no exception.

“This finding is intriguing and raises a number of questions, because evolutionary models of massive star cores do not predict the creation of neutron stars with masses lower than about 1.1 solar masses. This is the lowest mass estimated to date for a compact star” explain to Science and Future Christian Motch (CNRS, Strasbourg Astronomical Observatory), who did not participate in the study. “If it really is a neutron star, it allows for the first time to test equation of state models (the formulas that link the different parameters that characterize a star, pressure, temperature, density… Editor’s note) at low mass and significantly reduce the range of internal structures consistent with observations”. Considerable progress, but which raises new questions: “If it is indeed a star composed of neutrons, this would imply that a fairly strong mass loss phenomenon of unknown nature has taken place…” says Christian Motch.

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