[Paper Review] 3-Dimensional Core-Collapse

Chris L. Fryer, M. Warren|CERN Bulletin|Sep 19, 2003

Gamma-ray bursts and supernovae95 citations

TL;DR

This paper presents 3D hydrodynamic simulations of rotating massive star core-collapse, finding that rotation modifies convection above the proto-neutron star but does not cause core fragmentation or rapidly generate strong magnetic fields. Despite this, the most rapidly spinning models produce pulsars with enough rotational energy to dominate explosion energy, offering a potential constraint on progenitor rotation via gravitational wave signals and nucleosynthetic yields.

ABSTRACT

In this paper, we present the results of 3-dimensional collapse simulations of rotating stars for a range of stellar progenitors. We find that for the fastest spinning stars, rotation does indeed modify the convection above the proto-neutron star, but it is not fast enough to cause core fragmentation. Similarly, although strong magnetic fields can be produced once the proto-neutron star cools and contracts, the proto-neutron star is not spinning fast enough to generate strong magnetic fields quickly after collapse and, for our simulations, magnetic fields will not dominate the supernova explosion mechanism. Even so, the resulting pulsars for our fastest rotating models may emit enough energy to dominate the total explosion energy of the supernova. However, more recent stellar models predict rotation rates that are much too slow to affect the explosion, but these models are not sophisticated enough to determine whether the most recent, or past, stellar rotation rates are most likely. Thus, we must rely upon observational constraints to determine the true rotation rates of stellar cores just before collapse. We conclude with a discussion of the possible constraints on stellar rotation which we can derive from core-collapse supernovae.

Motivation & Objective

• To test whether rotation in massive stars alters core-collapse dynamics beyond spherical symmetry, particularly in convection and magnetic field generation.
• To assess whether rotational energy can power supernova explosions, especially in comparison to neutrino-driven mechanisms.
• To evaluate the potential for gravitational wave emission and asymmetric nucleosynthesis as observational constraints on progenitor rotation.
• To investigate the role of rotation in shaping pulsar spin and luminosity evolution post-explosion.
• To determine whether current stellar models overestimate or underestimate progenitor rotation rates based on observed supernova properties.

Proposed method

• Conduct 3D, fully $4\pi$-symmetric hydrodynamic simulations of rotating stellar cores using the FLASH code with simplified neutrino transport.
• Use a range of progenitor models with varying initial rotation rates (from slow to fast) to study rotational effects on collapse dynamics.
• Model the post-bounce evolution of proto-neutron stars, tracking convection, magnetic field amplification, and neutrino emission anisotropies.
• Simulate pulsar spin-down evolution using the formalism of Ho & Lai (2000), incorporating r-mode instabilities with varying amplitudes ($10^{-3}$ to $10^{-2}$).
• Compute gravitational wave strain amplitudes from asymmetric mass motions during collapse to assess detectability by advanced LIGO.
• Analyze neutrino-driven wind anisotropy and r-process nucleosynthesis yields to quantify rotational effects on nucleosynthetic output.

Experimental results

Research questions

• RQ1 Does rotation in massive stars significantly alter the convective dynamics above the proto-neutron star in 3D simulations?
• RQ2 Can rotational energy alone power supernova explosions, or is it insufficient compared to neutrino-driven mechanisms?
• RQ3 To what extent do rotational effects generate observable gravitational wave signals during core-collapse?
• RQ4 How do rotational asymmetries affect the anisotropy of neutrino emission and subsequent r-process nucleosynthesis?
• RQ5 Can pulsar spin-down evolution and luminosity provide constraints on the initial rotation rates of stellar progenitors?

Key findings

• Rotation modifies convection above the proto-neutron star in 3D simulations but is not fast enough to cause fragmentation of the iron core.
• Magnetic fields are amplified during proto-neutron star cooling, but not rapidly enough to dominate the explosion mechanism in the simulated models.
• The most rapidly rotating models produce pulsars whose rotational energy may exceed the total explosion energy, suggesting rotational energy could be a dominant energy source.
• Gravitational wave amplitudes from rotating models are up to five times stronger than in non-rotating cases, though still below detectability thresholds for advanced LIGO unless a galactic supernova occurs.
• Neutrino emission is anisotropic, with higher mean energies along the rotation poles due to deeper neutrinospheres, leading to asymmetric neutrino-driven winds and altered r-process yields.
• Pulsar luminosity and spin-down evolution are highly uncertain due to r-mode instability amplitudes; even with strong r-modes ($\alpha_{\rm r-mode} = 10^{-2}$), effects are negligible after 1000 years, making birth spin rates difficult to infer from observations.