Massive neutron stars have strange hearts

May 18, 2023

(Nanowerk News) After the cessation of nuclear fusion that characterizes the final phase of a star’s life, gravitational forces dominate the reduced pressure, potentially leading to the emergence of neutron stars – cosmic bodies consisting of the densest matter in the universe. The exact composition of these neutron stars, however, has sparked much scientific debate.

A pioneering investigation carried out by the team under the guidance of Professor FAN Yizhong of the Purple Mountain Observatory (PMO) of the Chinese Academy of Sciences (CAS) suggests the possible existence of a core of strange quark matter inside massive neutron stars, as proven by neutron star observations and the theory of quantum chromodynamics . This enigmatic core examination provides a unique opportunity to study the equations of state of solid matter and understand the transformation from hadronic matter to quarks.

The research findings are published in Science Bulletin (“The presence of a plausible new state in a neutron star with a mass above 0.98 MTOV).

In their analysis, the researchers used data on the mass and radius of the neutron star, gravitational wave information from binary neutron star mergers, and theoretical quantum chromodynamic constraints. Utilizing comprehensive data and new statistical methodologies, they undertook an in-depth exploration of the solid matter equations of state structures.

Their investigations found a characteristic peak structure in the speed of sound equation of state, which occurs at a density lower than that of the core of the heaviest neutron star. This anomaly implies a deviation from the purely hadronic state.

In addition, they found evidence supporting the existence of an exotic nucleus in a neutron star that exceeds 0.98 times the mass of the heaviest known neutron stars, proven by analyzes consistent with observational data and theoretical provisions.

Quantitative analysis shows that the state at the center of the heaviest neutron stars is softer than standard hadronic matter, even when considering the presence of hyperons. In doing so, the findings point to the possible existence of a significant exotic core extending more than 1 kilometer.

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