The simulation of the collapsing core of a star -- two shock waves move out and a core of quarks.
Entropy rendering of the second supernova shock generated by the first-order QCD phase transition, the original (stalled) supernova shock, and the beginning of the multidimensional motions in the core that generate the gravitational waves (Zha et al. 2020).

But now there are potentially new and powerful probes of supernova cores – gravitational waves and neutrinos, since they are generated in the stellar core and can penetrate matter with ease. However, the detection and understanding of these tracers relies on dedicated theoretical modeling and sophisticated computer simulations of possible scenarios for what might be happening.

One particularly interesting scenario is that since a collapsing supernova core can reach extremely high densities and temperatures, the protons and neutrons (particles forming atomic nuclei) there might break down into free quarks and gluons, much like water transforming to gas at high temperature. This transformation is dubbed the QCD phase transition (QCD, or Quantum ChromoDynamics, is the theory of the strong interaction between quarks and gluons). This phase transition can trigger a second collapse of the dying star's core.

In a paper recently published and selected as Editors’ suggestion in Physical Review Letters, OKC scientists Shuai Zha and Evan O'Connor and collaborators examine, for the first time, this QCD phase transition in core-collapse supernovae using state-of-the-art multi-dimensional supernova simulations. They report the unique imprints of such a phase transition on the emitted gravitational-wave and neutrino signals.

Distinguishable and new features of the emitted gravitational waves, such as high frequencies (~3000 Hz), large amplitudes, and short duration (less than 5 ms), emerge as a result of the QCD phase transition in the supernova core. Future detection of such a gravitational-wave signal, coincident with a burst of neutrinos, will provide strong evidence for the transformation of supernova core matter into quarks and gluons. Such a detection will also provide key information about the physics of core-collapse supernovae.