The influence of model parameters on the prediction of gravitational wave signals from stellar core collapse

We present the gravitational wave (GW) analysis of an extensive series of 3D MHD core-collapse simulations. Our 25 models are launched from a 15 solar mass progenitor, a spherically symmetric effective general relativistic potential, the Lattimer-Swesty or the Shen equation of state (EoS), and a neutrino parametrisation scheme which is accurate until about 5ms postbounce. For 3 representative models, we also include long-term neutrino physics by means of a leakage scheme. Non- or only slowly rotating models show GW emission due to prompt and proto-neutron star convection, allowing the distinction between the two different nuclear EoS. For moderately or fast rotation rates models, we find, in agreement with recent results, only a type I GW signature at core bounce. Models which are set up with an initial central angular velocity of >~ 2pi rad/s emit GWs due to the low T/|W| dynamical instability during the postbounce phase. Weak B-fields do not notably influence the dynamical evolution of the core and thus the GW emission. However, for strong initial poloidal B-fields (~1e12 G),flux-freezing and field winding leads to conditions where P_{mag}/P_{mat} ~ 1, causing the onset of a jet-like supernova explosion and hence the emission of a type IV GW signal. In contradiction to axisymmetric simulations, we find evidence that nonaxisymmetric fluid modes can counteract or even suppress jet formation for models with strong initial toroidal B-fields. We point out that the inclusion of the deleptonisation during the postbounce phase is an indispensable issue for the quantitative prediction of GWs from core-collapse supernovae, as it can alter the GW amplitude up to a factor of 10 compared to a pure hydrodynamical treatment.

💡 Research Summary

The paper presents a comprehensive three‑dimensional magnetohydrodynamic (MHD) study of gravitational‑wave (GW) emission from core‑collapse supernovae, based on 25 simulations that all start from a 15 M⊙ progenitor. An effective general‑relativistic potential is employed to mimic relativistic gravity, and two nuclear equations of state (Lattimer‑Swesty and Shen) are used to explore the influence of microphysics. A neutrino parametrisation scheme accurately treats deleptonisation up to ~5 ms after bounce; for three representative models a leakage scheme extends neutrino physics to later times.

The authors systematically vary three key parameters: (1) the initial rotation rate, ranging from non‑rotating to central angular velocities ≳2π rad s⁻¹; (2) the initial magnetic field geometry and strength, distinguishing weak fields, strong poloidal fields (~10¹² G), and strong toroidal fields; and (3) the equation of state. Their results reveal distinct GW signatures associated with each regime. Non‑ or slowly rotating models generate GW emission from prompt convection and proto‑neutron‑star (PNS) convection, and the subtle differences in the waveforms allow discrimination between the LS and Shen EOS. Moderately and rapidly rotating cores produce the classic type I bounce signal, while models with Ω₀ ≳ 2π rad s⁻¹ develop a low‑T/|W| dynamical instability after bounce, leading to an additional post‑bounce GW component.

Magnetic fields have a negligible effect on dynamics and GW emission when they are weak. However, strong initial poloidal fields (~10¹² G) become amplified by flux freezing and winding until magnetic pressure approaches matter pressure (Pₘₐg/Pₘₐt ≈ 1). This triggers a jet‑like explosion and a new type IV GW signal, distinct from the bounce‑driven type I waveform. In contrast, strong toroidal fields give rise to vigorous non‑axisymmetric fluid modes that can counteract or even suppress jet formation, a behavior not seen in axisymmetric studies and highlighting the importance of full 3‑D treatment.

A critical finding concerns neutrino physics: inclusion of post‑bounce deleptonisation dramatically changes GW amplitudes, with differences up to an order of magnitude compared to purely hydrodynamic runs. This underscores that accurate neutrino treatment is indispensable for quantitative GW predictions.

Overall, the study demonstrates that rotation, magnetic field configuration, nuclear EOS, and neutrino deleptonisation jointly determine the morphology, amplitude, and spectral content of core‑collapse GW signals. The identification of a type IV signal linked to magnetically driven jets, and the suppression of jets by non‑axisymmetric modes in toroidal‑field models, provide new diagnostics for interpreting future GW observations of supernovae.