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Register a new userA Neutrino-Driven Core Collapse Supernova Explosion of a 15 M Star
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We present results from an ab initio three-dimensional, multi-physics core collapse supernova simulation for the case of a 15 M progenitor. Our simulation includes multi-frequency neutrino transport with state-of-the-art neutrino interactions in the ray-by-ray approximation, and approximate general relativity. Our model exhibits a neutrino-driven explosion. The shock radius begins an outward trajectory at approximately 275 ms after bounce, giving the first indication of a developing explosion in the model. The onset of this shock expansion is delayed relative to our two-dimensional counterpart model, which begins at approximately 200 ms after core bounce. At a time of 441 ms after bounce, the angle-averaged shock radius in our three-dimensional model has reached 751 km. Further quantitative analysis of the outcomes in this model must await further development of the post-bounce dynamics and a simulation that will extend well beyond 1 s after stellar core bounce, based on the results for the same progenitor in the context of our two-dimensional, counterpart model. This more complete analysis will determine whether or not the explosion is robust and whether or not observables such as the explosion energy, 56Ni mass, etc. are in agreement with observations. Nonetheless, the onset of explosion in our ab initio three-dimensional multi-physics model with multi-frequency neutrino transport and general relativity is encouraging.
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Most supernova explosions accompany the death of a massive star. These explosions give birth to neutron stars and black holes and eject solar masses of heavy elements. However, determining the mechanism of explosion has been a half-century journey of great complexity. In this paper, we present our perspective of the status of this theoretical quest and the physics and astrophysics upon which its resolution seems to depend. The delayed neutrino-heating mechanism is emerging as a robust solution, but there remain many issues to address, not the least of which involves the chaos of the dynamics, before victory can unambiguously be declared. It is impossible to review in detail all aspects of this multi-faceted, more-than-half-century-long theoretical quest. Rather, we here map out the major ingredients of explosion and the emerging systematics of the observables with progenitor mass, as we currently see them. Our discussion will of necessity be speculative in parts, and many of the ideas may not survive future scrutiny. Some statements may be viewed as informed predictions concerning the numerous observables that rightly exercise astronomers witnessing and diagnosing the supernova Universe. Importantly, the same explosion in the inside, by the same mechanism, can look very different in photons, depending upon the mass and radius of the star upon explosion. A 10$^{51}$-erg (one Bethe) explosion of a red supergiant with a massive hydrogen-rich envelope, a diminished hydrogen envelope, no hydrogen envelope, and, perhaps, no hydrogen envelope or helium shell all look very different, yet might have the same core and explosion evolution.
We report on the gravitational wave signal computed in the context of a three-dimensional simulation of a core collapse supernova explosion of a 15 Solar mass star. The simulation was performed with our neutrino hydrodynamics code Chimera. We detail the gravitational wave strains as a function of time, for both polarizations, and discuss their physical origins. We also present the corresponding spectral signatures. Gravitational wave emission in our model has two key features: low-frequency emission (< 200 Hz) emanates from the gain layer as a result of neutrino-driven convection and the SASI and high-frequency emission (> 600 Hz) emanates from the proto-neutron star due to Ledoux convection within it. The high-frequency emission dominates the gravitational wave emission in our model and emanates largely from the convective layer itself, not from the convectively stable layer above it, due to convective overshoot. Moreover, the low-frequency emission emanates from the gain layer itself, not from the proto-neutron star, due to accretion onto it. We provide evidence of the SASI in our model and demonstrate that the peak of our low-frequency gravitational wave emission spectrum corresponds to it. Given its origin in the gain layer, we classify the SASI emission in our model as p-mode emission and assign a purely acoustic origin, not a vortical-acoustic origin, to it. Our dominant proto-neutron star gravitational wave emission is not well characterized by emission from surface g-modes, complicating the relationship between peak frequencies observed and the mass and radius of the proto-neutron star expressed by analytic estimates under the assumption of surface g-mode emission. We present our frequency normalized characteristic strain along with the sensitivity curves of current- and next-generation gravitational wave detectors.
We demonstrate that $sim10,textrm{s}$ after the core-collapse of a massive star, a thermonuclear explosion of the outer shells is possible for some (tuned) initial density and composition profiles, assuming that the neutrinos failed to explode the star. The explosion may lead to a successful supernova, as first suggested by Burbidge et al. We perform a series of one-dimensional (1D) calculations of collapsing massive stars with simplified initial density profiles (similar to the results of stellar evolution calculations) and various compositions (not similar to 1D stellar evolution calculations). We assume that the neutrinos escaped with a negligible effect on the outer layers, which inevitably collapse. As the shells collapse, they compress and heat up adiabatically, enhancing the rate of thermonuclear burning. In some cases, where significant shells of mixed helium and oxygen are present with pre-collapsed burning times of $lesssim100,textrm{s}$ ($approx10$ times the free-fall time), a thermonuclear detonation wave is ignited, which unbinds the outer layers of the star, leading to a supernova. The energy released is small, $lesssim10^{50},textrm{erg}$, and negligible amounts of synthesized material (including $^{56}$Ni) are ejected, implying that these 1D simulations are unlikely to represent typical core-collapse supernovae. However, they do serve as a proof of concept that the core-collapse-induced thermonuclear explosions are possible, and more realistic two-dimensional and three-dimensional simulations are within current computational capabilities.
We present self-consistent, axisymmetric core-collapse supernova simulations performed with the Prometheus-Vertex code for 18 pre-supernova models in the range of 11-28 solar masses, including progenitors recently investigated by other groups. All models develop explosions, but depending on the progenitor structure, they can be divided into two classes. With a steep density decline at the Si/Si-O interface, the arrival of this interface at the shock front leads to a sudden drop of the mass-accretion rate, triggering a rapid approach to explosion. With a more gradually decreasing accretion rate, it takes longer for the neutrino heating to overcome the accretion ram pressure and explosions set in later. Early explosions are facilitated by high mass-accretion rates after bounce and correspondingly high neutrino luminosities combined with a pronounced drop of the accretion rate and ram pressure at the Si/Si-O interface. Because of rapidly shrinking neutron star radii and receding shock fronts after the passage through their maxima, our models exhibit short advection time scales, which favor the efficient growth of the standing accretion-shock instability. The latter plays a supportive role at least for the initiation of the re-expansion of the stalled shock before runaway. Taking into account the effects of turbulent pressure in the gain layer, we derive a generalized condition for the critical neutrino luminosity that captures the explosion behavior of all models very well. We validate the robustness of our findings by testing the influence of stochasticity, numerical resolution, and approximations in some aspects of the microphysics.
We have been working within the fundamental paradigm that core collapse supernovae (CCSNe) may be neutrino driven, since the first suggestion of this by Colgate and White nearly five decades ago. Computational models have become increasingly sophisticated, first in one spatial dimension assuming spherical symmetry, then in two spatial dimensions assuming axisymmetry, and now in three spatial dimensions with no imposed symmetries. The increase in the number of spatial dimensions has been accompanied by an increase in the physics included in the models, and an increase in the sophistication with which this physics has been modeled. Computation has played an essential role in the development of CCSN theory, not simply for the obvious reason that such multidimensional, multi-physics, nonlinear events cannot possibly be fully captured analytically, but for its role in discovery. In particular, the discovery of the standing accretion shock instability (SASI) through computation about a decade ago has impacted all simulations performed since then. Today, we appear to be at a threshold, where neutrinos, neutrino-driven convection, and the SASI, working together over time scales significantly longer than had been anticipated in the past, are able to generate explosions, and in some cases, robust explosions, in a number of axisymmetric models. But how will this play out in three dimensions? Early results from the first three-dimensional (3D), multi-physics simulation of the Oak Ridge group are promising. I will discuss the essential components of todays models and the requirements of realistic CCSN modeling, present results from our one-, two-, and three-dimensional models, place our models in context with respect to other efforts around the world, and discuss short- and long-term next steps.
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