paper

Plausible presence of new state in neutron stars with masses above

arXiv:2207.13613 · doi:10.1016/j.scib.2023.04.007

Abstract

We investigate the neutron star (NS) equation of state (EOS) by incorporating multi-messenger data of GW170817, PSR J0030+0451, PSR J0740+6620, and state-of-the-art theoretical progresses, including the information from chiral effective field theory (EFT) and perturbative quantum chromodynamics (pQCD) calculation. Taking advantage of the various structures sampling by a single-layer feed-forward neural network model embedded in the Bayesian nonparametric inference, the structure of NS matter's sound speed is explored in a model-agnostic way. It is found that a peak structure is common in the posterior, locating at (nuclear saturation density) and exceeds at 90\% credibility. The non-monotonic behavior suggests evidence of the state deviating from hadronic matter inside the very massive NSs. Assuming the new/exotic state is featured as it is softer than typical hadronic models or even with hyperons, we find that a sizable () exotic core, likely made of quark matter, is plausible for the NS with a gravitational mass above about , where represents the maximum gravitational mass of a non-rotating cold NS. The inferred (90\% credibility) is well consistent with the value of estimated independently with GW170817/GRB 170817A/AT2017gfo assuming a temporary supramassive NS remnant formed after the merger. PSR J0740+6620, the most massive NS detected so far, may host an exotic core with a probability of .

arXiv comment8+5 pages, 6+5 figures, published in Science Bulletin

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