| Popis: |
During the core‐collapse of a massive star, the spherical accretion shock which stalls at about 150km above the surface of the newly formed neutron star is hydrodynamically unstable. A perturbative approach has allowed us to disentangle the effects of neutrino‐driven convection from those of the advective‐acoustic instability. The large scale, l = 1 asymmetry appearing a few hundred millisecond after core bounce cannot be explained by negative‐entropy gradients due to neutrino heating in the gain region. This asymmetry is a natural consequence of the advective‐acoustic cycle, occurring between the shock and the region of deceleration associated with neutrino cooling above the neutrinosphere. A detailed stability analysis of the flow has proven the instability of the advective‐acoustic cycle in the simplified set up studied numerically by Blondin & Mezzacappa (2006, 2007). Our analysis also suggests that the purely acoustic cycle is stable. |
