Mémoire
| Résumé : | Formed in the aftermath of gravitational core-collapse supernova explosions, neutron stars contain matter crushed at densities exceeding those found inside atomic nuclei and are therefore unique laboratories for exploring novel phases of matter under conditions so extreme that they cannot be experimentally reproduced on Earth. Although most neutron stars are endowed with typical magnetic fields of order 1E12 G, the subclass of magnetars exhibits much higher fields, of order 1E14 − 1E15 G at their surface, and potentially much stronger in their interior. The recent detections of spin frequency “glitches” in some magnetars associated with fast radio bursts and pulsed radio emissions suggest the existence of some internal processes as the likely origin of these phenomena. This Master’s thesis aims to investigate the nature of these processes by considering magnetically-driven volcanic and seismic activities. First, an analytical mathematical model will be developed to describe the outer crust of a magnetar. Numerical calculations will be carried out to follow the change in composition of the outer crust as a function of the magnetic field. To this end, the HFB-24 atomic mass model developed by the Brussels-Montreal group will be used, supplemented with experimental data. The effect of the magnetic field on nuclear masses and their consequences on pressures and densities in the crust will then be analyzed. Subsequently, the stability of the matter forming the outer crust will be studied. As the magnetic field of a magnetar decays, the hydrostatic equilibrium of the crust is altered, potentially triggering electron captures and delayed neutron emissions. Under certain conditions, these reactions could lead to a form of volcanism, involving the ejection of neutron-rich matter in a strong wind, and crustquakes, triggered by the contraction of the crust following electron captures. The conditions under which such events may occur will be determined, and numerical estimates will be obtained to assess whether these volcanic and seismic activities can account for astrophysical observations. |
