• Citer

The decompression of the outer neutron star crust and r-process nucleosynthesis

par Goriely, Stéphane ;Chamel, Nicolas ;Janka, Hans-Thomas;Pearson, Michael J.
Référence Astronomy & astrophysics, 531, A78
Publication Publié, 2011-06-15

Article révisé par les pairs

• Accès en ligne
• Détails
• Contenu
• Statistiques

Résumé :

Context. The rapid neutron-capture process, or r-process, is known to be fundamental for explaining the origin of approximately half of the A > 60 stable nuclei observed in nature. In recent years nuclear astrophysicists have developed more and more sophisticated r-process models, by adding new astrophysical or nuclear physics ingredients to explain the solar system composition in a satisfactory way. Despite these efforts, the astrophysical site of the r-process remains unidentified.Aims. The composition of the neutron star outer crust material is investigated after the decompression that follows its possible ejection.Methods. The composition of the outer crust of a neutron star is estimated before and after decompression. Two different possible initial conditions are considered, namely an idealized crust composed of cold catalyzed matter and a crust initially in nuclear statistical equilibrium at temperatures around 10^10 K.Results. We show that in this second case before decompression and at temperatures typically corresponding to 8 x 10^9 K, the Coulomb effect owing to the high densities in the crust leads to an overall composition of the outer crust in neutron-rich nuclei with a mass distribution close to the solar system r-abundance distribution. Such distributions differ, however, from the solar one due to a systematic shift in the second peak to lower values. After decompression, the capture of the few neutrons per seed nucleus available in the hot outer crust leads to a final distribution of stable neutron-rich nuclei with a mass distribution of 80 ≤ A ≤ 140 nuclei in excellent agreement with the solar distribution, provided the outer crust is initially at temperatures around 8 x 10^9 K and all layers of the outer crust are ejected.Conclusions. The decompression of the neutron star matter from the outer crust provides suitable conditions for a robust r-processing of the light species, i.e., r-nuclei with A ≤ 140. The final composition should carry the imprint of the temperature at which the nuclear statistical equilibrium is frozen prior to the ejection.