The Explosion Mechanism of Core-Collapse Supernovae: Progress in Supernova Theory and Experiments

Abstract

The explosion of core-collapse supernova depends on a sequence of events taking place in less than a second in a region of a few hundred kilometers at the centre of a supergiant star, after the stellar core approaches the Chandrasekhar mass and collapses into a proto-neutron star, and before a shock wave is launched across the stellar envelope. Theoretical efforts to understand stellar death focus on the mechanism which transforms the collapse into an explosion. Progress in understanding this mechanism is reviewed with particular attention to its asymmetric character. We highlight a series of successful studies connecting observations of supernova remnants and pulsars properties to the theory of corecollapse using numerical simulations. The encouraging results from first principles models in axisymmetric simulations is tempered by new puzzles in 3D. The diversity of explosion paths and the dependence on the pre-collapse stellar structure is stressed, as well as the need to gain a better understanding of hydrodynamical and MHD instabilities such as standing accretion shock instability and neutrino-driven convection. The shallow water analogy of shock dynamics is presented as a comparative system where buoyancy effects are absent. This dynamical system can be studied numerically and also experimentally with a water fountain. The potential of this complementary research tool for supernova theory is analysed. We also review its potential for public outreach in science museums.

Supernovae from Massive Stars

“…These simple hydrodynamic simulations are needed because, to date, there is no well-established self-consistent 3D model that naturally obtains the explosion of core collapse supernovae with their typical observed prop- erties [42]. These "simplified" explosions are artificially induced by injecting in the presupernova model some amount of energy in an also arbitrary mass location (typically near the edge of the iron core) and followed by means of a 1D hydro code.…”

Neutrino-Driven Explosions

“…Since neutrino-energy deposition creates a negative entropy gradient, the heated layer can become convectively unstable (Herant et al, 1994;Burrows et al, 1995;Janka and Müller, 1996;Foglizzo et al, 2006). Also the standing-accretion-shock instability (SASI; Blondin et al, 2003;Blondin and Mezzacappa, 2007;Scheck et al, 2008;Foglizzo et al, 2015) can grow in the mass-accretion flow between shock and nascent NS, leading to large-scale, nonradial deformation and violent sloshing and spiral motions of the shock front, thus stirring the whole layer enclosed by the shock and the NS. Mushroom-like highentropy structures indicative of buoyancy-driven Rayleigh-Taylor instability can be seen in the postshock region in the middle-right panel of Fig.…”

“…These considerations are only qualitative order-of-magnitude estimates. The relative importance of convection and the SASI in building up and storing non-radial kinetic energy in the postshock layer, their detailed roles in the revival of the stalled SN shock, and the exact differences between 2D and 3D dynamics remain topics of vivid debate (for reviews, see Janka et al 2016, Müller 2016, and Foglizzo et al 2015 for examples of conflictive points of view, see also Burrows et al 2012;Fernández 2015;Cardall and Budiardja 2015). Controversies are often based on simplified numerical models, but conclusive answers for the SN-core dynamics on the way to a successful explosion require fully self-consistent 3D simulations.…”

Inferring the core-collapse supernova explosion mechanism with gravitational waves

“…Observations of CCSN ejecta and pulsar kicks are indicative of the multidimensional physical processes driving the explosion [5,6].…”