טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentAvishai Gilkis
SubjectIntermittent Accretion disk Production in Core Collapse
Supernovae
DepartmentDepartment of Physics
Supervisor Full Professor Soker Noam
Full Thesis textFull thesis text - English Version


Abstract

Core-collapse supernovae (CCSNe) occur after the iron core of a massive star reaches a critical mass, although the detailed mechanism of the explosion remains unknown. The well-studied delayed neutrino-heating mechanism is the most popular in the literature, but it fails to supply the observed energy or even achieve an explosion at all. An alternative to the neutrino-driven explosion is a jet-driven mechanism for CCSNe. In my research I studied the sources of angular momentum required for such a mechanism in slowly and rapidly rotating massive stars. Estimating the stochastic angular momentum in convective regions of massive stars with analytic approximations applied to stellar models, I find significant angular momentum fluctuations in the helium shell. I further study the convective helium shell with sub-sonic hydrodynamic simulations, reinforcing the analytic estimations. This implies a possible ‘jittering jets’ mechanism where the jets are fueled by accretion from the helium shell onto a black hole, due to the high enclosed mass of the inner iron core and silicon and oxygen shells. I study the case of rapid rotation with hydrodynamic simulations including approximate neutrino transport, where an accretion disk forms around a rapidly spinning neutron star during collapse. I hypothesize that rare rapidly-rotating stars collapsing in this manner are progenitors of super-luminous supernovae, and also contribute to the synthesis of elements with high mass numbers due to the neutron-rich accretion disk. Overall, my results support a paradigm of continuous CCSN explosions, arising from the varying pre-collapse conditions of different massive stars. The rate of rotation may be the most important parameter, with slow rotation resulting in regular CCSNe, and fast rotation bringing about more energetic explosions. Long duration gamma-ray bursts accompanying CCSNe may be an extreme limit of very fast rotation.