[Paper Review] Thermonuclear explosion of rotating massive stars could explain core-collapse supernovae

Doron Kushnir|arXiv (Cornell University)|Feb 10, 2015

Gamma-ray bursts and supernovae18 citations

TL;DR

This paper proposes that core-collapse supernovae (CCSNe) are driven by thermonuclear detonation waves ignited in rotating, massive stars with slowly rotating, mixed helium-oxygen shells. Two-dimensional hydrodynamic simulations show that such configurations lead to robust, energetic explosions with kinetic energies of 10⁴⁹–10⁵² erg and ⁵⁶Ni yields up to ~1 M☉, matching observed CCSNe properties and explaining the correlation between explosion energy and ⁵⁶Ni mass.

ABSTRACT

It is widely thought that core-collapse supernovae (CCSNe), the explosions of massive stars following the collapse of the stars' iron cores, is obtained due to energy deposition by neutrinos. So far, this scenario was not demonstrated from first principles. Kushnir and Katz (2014) have recently shown, by using one-dimensional simulations, that if the neutrinos failed to explode the star, a thermonuclear explosion of the outer shells is possible for some (tuned) initial profiles. However, the energy released was small and negligible amounts of ejected $^{56}$Ni were obtained, implying that these one-dimensional collapse induced thermonuclear explosions (CITE) are unlikely to represent typical CCSNe. Here I provide evidence supporting a scenario in which the majority of CCSNe are the result of CITE. I use two-dimensional simulations to show that collapse of stars that include slowly (few percent of breakup) rotating $\sim0.1-10\,M_{\odot}$ shells of mixed helium-oxygen, leads to an ignition of a thermonuclear detonation wave that unbinds the stars' outer layers. Simulations of massive stars with different properties show that CITE is a robust process, and results in explosions with kinetic energies in the range of $10^{49}-10^{52}\, extrm{erg}$, and $^{56}$Ni yields of up to $\sim\,M_{\odot}$, which are correlated, in agreement with observations for the majority of CCSNe. Stronger explosions are predicted from higher mass progenitors that leave more massive remnants, in contrast to the neutrino mechanism. Neutron stars are produced in weak ($\lt10^{51}\, extrm{erg}$) explosions, while strong ($\gt10^{51}\, extrm{erg}$) explosions leave black hole remnants.

Motivation & Objective

• To resolve the long-standing problem of how core-collapse supernovae achieve observed explosion energies (~10⁵¹ erg) and ⁵⁶Ni masses.
• To test whether collapse-induced thermonuclear explosions (CITE) can explain typical CCSNe, given that previous one-dimensional models failed to produce sufficient energy or ⁵⁶Ni.
• To investigate the role of rotation and composition (specifically He-O mixtures) in enabling robust detonation ignition during core collapse.
• To determine the conditions under which CITE produces explosions consistent with observed correlations between kinetic energy and ⁵⁶Ni mass in CCSNe.
• To predict the remnant mass (neutron star vs. black hole) as a function of explosion energy, contrasting with the neutrino-driven mechanism.

Proposed method

• Two-dimensional, fully resolved hydrodynamic simulations using the CASTRO code to model the collapse and explosion of massive stars with rotating He-O shells.
• Initial profiles are constructed with constant entropy, composition, and hydrostatic equilibrium, including a 1.2 M☉ iron core and a 0.1–10 M☉ He-O shell with densities ~few × 10³ g cm⁻³.
• The simulations track the evolution of thermodynamic and nuclear energy release, focusing on the ignition and propagation of a thermonuclear detonation wave.
• The critical parameter is the ratio of burning time to free-fall time (t_b/t_ff) at the base of the He-O shell, which determines the likelihood of detonation ignition.
• The presence of mixed helium-oxygen is identified as essential for detonation ignition, as prior studies without such mixtures failed to produce explosions.
• Explosion energy and ⁵⁶Ni yield are calculated from post-explosion ejecta, and their correlation is compared to observational data from light curves.

Experimental results

Research questions

• RQ1 Can collapse-induced thermonuclear explosions (CITE) in rotating massive stars produce explosions with kinetic energies and ⁵⁶Ni yields matching observed core-collapse supernovae?
• RQ2 What role does the presence of a mixed helium-oxygen shell play in enabling detonation ignition during core collapse?
• RQ3 Is the CITE mechanism robust to variations in initial profile parameters such as shell mass, density, and rotation rate?
• RQ4 Does the CITE mechanism naturally explain the observed correlation between kinetic energy and ⁵⁶Ni mass in CCSNe?
• RQ5 Can the CITE mechanism predict whether a supernova remnant will be a neutron star or black hole based on explosion energy?

Key findings

• Two-dimensional simulations demonstrate that slowly rotating (few percent of breakup speed) massive stars with 0.1–10 M☉ He-O shells ignite a thermonuclear detonation wave, unbinding the outer layers.
• The resulting explosions have kinetic energies in the range 10⁴⁹–10⁵² erg, matching the observed energy distribution of core-collapse supernovae.
• ⁵⁶Ni yields reach up to ~1 M☉, with a strong correlation between kinetic energy and ⁵⁶Ni mass, consistent with observational light curve data.
• Stronger explosions (≥10⁵¹ erg) are predicted from higher mass progenitors and lead to black hole remnants, while weaker explosions (<10⁵¹ erg) produce neutron stars.
• The presence of mixed helium-oxygen is a necessary condition for detonation ignition; previous studies without such mixtures failed to produce explosions.
• The CITE mechanism is robust across a wide range of initial profiles, indicating it is a viable and general explanation for the majority of core-collapse supernovae.