Unveiling Neutron Star Secrets: Two-Dimensional Insights into Nuclear Matter

Researchers at Brookhaven National Laboratory have utilized principles from two-dimensional condensed matter physics to gain a deeper understanding of quark interactions within neutron stars. This novel approach simplifies the study of these incredibly dense cosmic entities, shedding light on low-energy excitations in dense nuclear matter and potentially uncovering new phenomena in extreme densities. As a result, advancements in neutron star research and comparisons with heavy-ion collisions may be propelled forward.

The Study

The intricate behavior of nuclear matter, comprising quarks and gluons that constitute atomic nuclei’s protons and neutrons, presents a considerable challenge for comprehension. This challenge is particularly complex within our three-dimensional world. By applying mathematical techniques derived from condensed matter physics that consider interactions within a single spatial dimension (alongside time), scientists have significantly simplified the endeavor. Through this two-dimensional framework, researchers have successfully solved intricate equations describing the propagation of low-energy excitations within dense nuclear matter systems. Intriguingly, this work suggests that the core of neutron stars, where such extraordinarily dense nuclear matter naturally exists, might possess an unexpected nature.

The Significance

Understanding quark interactions within two dimensions provides a fresh perspective on neutron stars, which represent the densest known form of matter in the universe. This approach holds the potential to contribute to the ongoing “golden age” of neutron star studies, which has been stimulated by recent discoveries of gravitational waves and electromagnetic emissions in the cosmos. Notably, this research reveals that the complexities associated with three-dimensional quark interactions largely disappear when considering low-energy excitations. These excitations manifest as subtle disturbances triggered by radiation emissions from a neutron star or its own spinning magnetic fields. Moreover, this approach could facilitate new comparisons between quark interactions within less dense yet significantly hotter nuclear matter generated in heavy-ion collisions.

Summary

Quantum chromodynamics, the contemporary theory of nuclei, revolves around quarks bound by the strong nuclear force, which is mediated by gluons. These forces confine quarks into nucleons such as protons and neutrons. As the density of nuclear matter increases within neutron stars, the system begins to behave more like a mass of quarks, with blurred boundaries between individual nucleons. In this state, quarks on the system’s edge remain confined by the strong force, enabling strong interactions between quarks located on opposite sides of the spherical system.

The research conducted at Brookhaven National Laboratory leverages the one-dimensional nature of these strong interactions, in addition to the dimension of time, to comprehend low-energy excitations near the system’s edge. These low-energy modes closely resemble those of a free, massless boson—referred to as a “Luttinger liquid” in condensed matter physics. This method empowers scientists to calculate the parameters of a Luttinger liquid at any given density. Consequently, it enhances their ability to explore qualitatively novel phenomena that are expected to arise within neutron stars’ extreme densities, where nuclear matter behaves distinctly compared to ordinary nuclei. Moreover, it allows for comparisons with much hotter (trillion-degree) dense nuclear matter generated in heavy-ion collisions.

Reference: “When cold, dense quarks in 1+1 and 3+1 dimensions are not a Fermi liquid” by Marton Lajer, Robert M. Konik, Robert D. Pisarski and Alexei M. Tsvelik, 30 March 2022, Physical Review D.
DOI: 10.1103/PhysRevD.105.054035

This research received funding from the Department of Energy Office of Science.

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• Brookhaven National Laboratory
• Physical Review D: “When cold, dense quarks in 1+1 and 3+1 dimensions are not a Fermi liquid”