Gravitational Waves as a Probe of Core Collapse Supernova Progenitor Structure

TL;DR

This paper addresses whether gravitational waves can reveal a CCSN progenitor's internal structure by comparing two nearly identical $M_\odot$ progenitors with different density profiles and compactness, characterized by $ξ_{2.5}$. Using two-dimensional Chimera simulations, the authors extract GW signals from matter motion and anisotropic neutrino emission, incorporating a low-pass filter to mitigate numerical artifacts and defining the gfF (g-/f-mode) frequency evolution via a linear fit $f(t)=\alpha t+\beta$ with $\alpha$ values of $1789$ and $2263\ \text{Hz s}^{-1}$ for the less and more compact models, respectively. They find that the more compact model, $ξ_{2.5}=0.206$, exhibits larger GW strains and energy and a faster gfF evolution, consistent with a faster PNS contraction and stronger postbounce accretion, while the less compact model shows weaker high-frequency content. This demonstrates, in principle, that gravitational-wave detections can constrain interior stellar structure, though the results are limited to 2D and would benefit from 3D confirmation and systematic control of other progenitor differences.

Abstract

We present the gravitational wave predictions from two-dimensional core collapse supernova (CCSN) simulations initiated from two nearly identical progenitors that have significantly different internal structures due to their late-stage stellar evolution. At the time of collapse, the 15.78 $M_{\odot}$ and 15.79 $M_{\odot}$ progenitors have compactness parameters $ξ_{2.5}$ of 0.136 and 0.206, respectively. We connect several features of the gravitational wave signal from each model to its previously explored explosion dynamics. In particular, the greater accretion onto the PNS of the more compact model is evident in broad-band frequency features with larger amplitude gravitational wave strains and greater gravitational wave energy release when compared to the less compact model. Additionally, the faster contraction rate of the more compact model is reflected in the $\sim$26% greater slope of the $g$-/$f$-mode feature (gfF) evolution of the gravitational wave signal. This work shows that in principle gravitational wave detection may provide information about interior stellar structure.

Figures (12)

• Figure 1: Angle-integrated energy luminosity of neutrinos passing through a sphere of radius 500 km (top) and anisotropy parameter (bottom) for each model. For each quantity, neutrino species are denoted by color, with orange for electron neutrinos, yellow for anti-electron neutrinos, purple for heavy neutrinos ($\mu+\tau$ neutrinos), and light blue for anti-heavy neutrinos. Dark blue indicates the total luminosity/anisotropy from all neutrino species.
• Figure 2: $h_+$-polarized strains multiplied by a distance of 10 kpc as viewed from the $z$-axis of the simulation for F15.78 (purple) and F15.79 (teal). The strain for the first 150 ms after bounce is shown, with a modified vertical axis, in the inset plot.
• Figure 3: Plot of electron fraction within the inner 50 km of the star for F15.78 (left) and F15.79 (right). The top panels are shown at 7 ms for F15.78 and 12 ms for F15.79. The bottom panels are shown at 106 ms for F15.78 and 100 ms for F15.79. The color axis represents electron fraction, and the pink contour corresponds to the outer boundary of Region I.
• Figure 4: Specific entropy in and around the PNS for F15.78 (left) and F15.79 (right). The purple contour denotes the $10^{10}$ g cm$^{-3}$ spherically-averaged density contour (i.e., outside the PNS) and the pink contour denotes the $10^{12}$ g cm$^{-3}$ spherically-averaged density contour (i.e., deep inside the PNS).Top panels show plots at 190 ms and 244 ms after bounce for F15.78 and F15.79, respectively. Bottom panels show plots at 756 ms and 664 ms after bounce for F15.78 and F15.79, respectively.
• Figure 5: Entropy snapshots for F15.78 at 442 ms and 1258 ms, respectively, displaying key hydrodynamic features that contribute to the evolution of the memory resulting from the matter outflows.