In this paper, we present a new mechanism for core-collapse supernova explosions that relies upon acoustic power generated in the inner core as the driver. In our simulation using an 11-M ⊙ progenitor, an advective-acoustic oscillationà la Foglizzo with a period of ∼25−30 milliseconds (ms) arises ∼200 ms after bounce. Its growth saturates due to the generation of secondary shocks, and kinks in the resulting shock structure funnel and regulate subsequent accretion onto the inner core. However, this instability is not the primary agent of explosion. Rather, it is the acoustic power generated early on in the inner turbulent region stirred by the accretion plumes, and most importantly, but later on, by the excitation and sonic damping of core g-mode oscillations. An ℓ = 1 mode with a period of ∼3 ms grows at late times to be prominent around ∼500 ms after bounce. The accreting protoneutron star is a self-excited oscillator, "tuned" to the most easily excited core g-mode. The associated acoustic power seen in our 11-M ⊙ simulation is sufficient to drive the explosion >550 milliseconds after bounce. The angular distribution of the emitted sound is fundamentally aspherical. The sound pulses radiated from the core steepen into shock waves that merge as they propagate into the outer mantle and deposit their energy and momentum with high efficiency. The ultimate source of the acoustic power is the gravitational energy of infall and the core oscillation acts like a transducer to convert this accretion energy into sound. An advantage of the acoustic mechanism is that acoustic power does not abate until accretion subsides, so that it is available as long as it may be needed to explode the star. This suggests a natural means by which the supernova is self-regulating.

We present here the first 2D rotating, multi-group, radiation magnetohydrodynamics (RMHD) simulations of supernova core collapse, bounce, and explosion. In the context of rapid rotation, we focus on the dynamical effects of magnetic stresses and the creation and propagation of MHD jets. We find that a quasi-steady state can be quickly established after bounce, during which a well-collimated MHD jet is maintained by continuous pumping of power from the differentially rotating core. If the initial spin period of the progenitor core is < ∼ 2 seconds, the free energy reservoir in the secularly evolving protoneutron star is adequate to power a supernova explosion, and may be enough for a hypernova. The jets are well collimated by the infalling material and magnetic hoop stresses, and maintain a small opening angle. We see evidence of sausage instabilities in the emerging jet stream. Neutrino heating is sub-dominant in the rapidly rotating models we explore, but can contribute 10−25% to the final explosion energy. Our simulations suggest that even in the case of modest or slow rotation, a supernova explosion might be followed by a secondary, weak MHD jet explosion, which, because of its weakness may to date have gone unnoticed in supernova debris. Furthermore, we suggest that the generation of a non-relativistic MHD precursor jet during the early protoneutron star/supernova phase is implicit in both the collapsar and "millisecond magnetar" models of GRBs. The multi-D, multi-group, rapidly rotating RMHD simulations we describe here are a start along the path towards more realistic simulations of the possible role of magnetic fields in some of Nature's most dramatic events.

We present VULCAN/2D multigroup flux-limited-diffusion radiation-hydrodynamics simulations of binary neutron star mergers, using the Shen equation of state, covering 100 ms, and starting from azimuthal-averaged twodimensional slices obtained from three-dimensional smooth-particle-hydrodynamics simulations of Rosswog & Price for 1.4 M (baryonic) neutron stars with no initial spins, co-rotating spins, or counter-rotating spins. Snapshots are post-processed at 10 ms intervals with a multiangle neutrino-transport solver. We find polarenhanced neutrino luminosities, dominated byν e and "ν μ " neutrinos at the peak, although ν e emission may be stronger at late times. We obtain typical peak neutrino energies for ν e ,ν e , and "ν μ " of ∼ 12, ∼ 16, and ∼ 22 MeV, respectively. The supermassive neutron star (SMNS) formed from the merger has a cooling timescale of 1 s. Charge-current neutrino reactions lead to the formation of a thermally driven bipolar wind with Ṁ ∼ 10 −3 M s −1 and baryon-loading in the polar regions, preventing any production of a γ -ray burst prior to black hole formation. The large budget of rotational free energy suggests that magneto-rotational effects could produce a much-greater polar mass loss. We estimate that 10 −4 M of material with an electron fraction in the range 0.1-0.2 becomes unbound during this SMNS phase as a result of neutrino heating. We present a new formalism to compute the ν iνi annihilation rate based on moments of the neutrino-specific intensity computed with our multiangle solver. Cumulative annihilation rates, which decay as ∼t −1.8 , decrease over our 100 ms window from a few ×10 50 to ∼ 10 49 erg s −1 , equivalent to a few ×10 54 to ∼ 10 53 e − e + pairs per second.

Type Ia supernovae (SNe Ia), thermonuclear explosions of carbon-oxygen white dwarfs (CO-WDs), are currently the best cosmological "standard candles", but the triggering mechanism of the explosion is unknown. It was recently shown that the rate of head-on collisions of typical field CO-WDs in triple systems may be comparable to the SNe Ia rate. Here we provide evidence supporting a scenario in which the majority of SNe Ia are the result of such head-on collisions of CO-WDs. In this case, the nuclear detonation is due to a well understood shock ignition, devoid of commonly introduced free parameters such as the deflagration velocity or transition to detonation criteria. By using two-dimensional hydrodynamical simulations with a fully resolved ignition process, we show that zero-impact-parameter collisions of typical CO-WDs with masses 0.5 − 1 M ⊙ result in explosions that synthesize 56 Ni masses in the range of ∼ 0.1 − 1 M ⊙ , spanning the wide distribution of yields observed for the majority of SNe Ia. All collision models yield the same late-time ( ∼ > 60 days since explosion) bolometric light curve when normalized by 56 Ni masses (to better than 30%), in agreement with observations. The calculated widths of the 56 Ni-mass-weighted-line-of-sight velocity distributions are correlated with the calculated 56 Ni yield, agreeing with the observed correlation. The strong correlation, shown here for the first time, between 56 Ni yield and total mass of the colliding CO-WDs (insensitive to their mass ratio), is suggestive as the source for the continuous distribution of observed SN Ia features, possibly including the Philips relation.

We present 2.5-dimensional radiation-hydrodynamics simulations of the accretion-induced collapse (AIC ) of white dwarfs, starting from two-dimensional rotational equilibrium configurations, thereby accounting consistently for the effects of rotation prior to and after core collapse. We focus our study on a 1.46 and a 1.92 M a model. Electron capture leads to the collapse to nuclear densities of these cores a few tens of milliseconds after the start of the simulations. The shock generated at bounce moves slowly, but steadily, outward. Within 50-100 ms, the stalled shock breaks out of the white dwarf along the poles. The blast is followed by a neutrino-driven wind that develops within the white dwarf, in a cone of $40 opening angle about the poles, with a mass loss rate of (5 8) ; 10 À3 M s À1 . The ejecta have an entropy on the order of (20-50) k B baryon À1 and an electron fraction that is bimodal. By the end of the simulations, at k600 ms after bounce, the explosion energy has reached (3 4) ; 10 49 ergs and the mass has reached a few times 10 À3 M . We estimate the asymptotic explosion energies to be lower than 10 50 ergs, significantly lower than those inferred for standard core collapse. The AIC of white dwarfs thus represents one instance where a neutrino mechanism leads undoubtedly to a successful, albeit weak, explosion. We document in detail the numerous effects of the fast rotation of the progenitors: the neutron stars are aspherical; the '' '' and¯e neutrino luminosities are reduced compared to the e neutrino luminosity; the deleptonized region has a butterfly shape; the neutrino flux and electron fraction depends strongly upon latitude (a la von Zeipel ); and a quasi-Keplerian 0.1-0.5 M accretion disk is formed.