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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.
Institut de Physique Nucléaire Orsay - 15 rue Georges CLEMENCEAU - 91406 ORSAY (FRANCE) |
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