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Astrophysique nucléaire

There are also many interfaces between nuclear physics and astrophysics, the most prominent being questions related to supernova explosions, the synthesis of elements, and neutron stars. 

Type II supernovae occur at the end of the life of a star, but they are not yet fully understood ; even in the most sophisticated simulations, the shock wave formed after the collapse of the star is insufficient to cause the star to explode. For the understanding of supernovae, the equation of state of dense matter is not the only relevant nuclear-physics input ; nuclear electron-capture cross sections have been, for instance, studied in our group. They determine the electron fraction and hence the pressure in the core of the star in the pre-supernova stage, and the neutronization during the supernova explosion.

Explosions of intermediate-mass stars leave behind neutron stars. By now, thousands of such stars have been discovered and properties like rotation period, mass, radius, temperature, age and magnetic field are known for many of them. Models developed to describe properties of nuclei can be applied to understand dilute nuclei in the crust of neutrons stars within the Wigner-Seitz approximation. The superfluid properties of the crust, as well as the effect of huge magnetic fields of the order of 1018 Gauss that might be present in magnetars, are studied. The recent observation of a neutron star with two solar masses gives strong constraints on the equation of state in the core. In particular, at high densities, one expects that hyperons will appear in addition to neutrons and protons ; this softens the equation of state, making it impossible to sustain such a massive star.


 

IPN

Institut de Physique Nucléaire Orsay - 15 rue Georges CLEMENCEAU - 91406 ORSAY (FRANCE)
UMR 8608 - CNRS/IN2P3

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