Abstract
With recent advances in neutron star observations, major progress has been made in determining the pressure of neutron star matter at high density. This pressure is constrained by the neutron star deformability, as determined from gravitational waves emitted in a neutron star merger, and measurements of the radii of two neutron stars made using the Neutron Star Interior Composition Explorer X-ray observatory on the International Space Station. Previous studies have relied on nuclear theory calculations to provide the equation of state at low density. Here we use a combination of 15 constraints composed of three astronomical observations and 12 nuclear experimental constraints that extend over a wide range of densities. Bayesian inference is then used to obtain a comprehensive nuclear equation of state. This data-centric result provides benchmarks for theoretical calculations and modelling of nuclear matter and neutron stars. Furthermore, it provides insights into the composition of neutron stars and their cooling due to neutrino radiation.
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Code availability
Analysis codes specially written for this work are available online at https://github.com/nscl-hira/TidalPolarizabilityPublic. The TOV solver used in this work is available upon request to the corresponding author.
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Acknowledgements
We would like to acknowledge many stimulating discussions with the participants at the workshops sponsored by the Institute of Nuclear Theory in 2021 and 2022 and with members of the Transport Model Evaluation Project. We are grateful to C. Drischler for providing the χEFT calculations shown in our figures. This work is supported in part by the National Science Foundation (Grant No. PHY-2209145 to R.K., W.G.L., C.Y.T. and M.B.T.) and the US Department of Energy, Office of Science, Office of Nuclear Physics (Grant No. DE-FG02-87ER40365 to C.J.H.). The Facility for Radioactive Ion Beams (FRIB), funded by the US Department of Energy, is committed to fostering a safe, diverse, equitable and inclusive work and research environment in which respect and personal integrity are valued. We adhere to the FRIB research code of conduct in accordance with the highest scientific, professional and ethical standards, as detailed in https://frib.msu.edu/users/pac/conduct.html. In an ideal world, it should not be necessary to identify the authors by gender or from under-represented group. Until the ideal world is reached, we acknowledge that our references and citations most likely under-represent contributions from women and minorities. We further acknowledge that Michigan State University occupies the ancestral, traditional and contemporary lands of the Anishinaabeg and the Three Fires Confederacy of the Ojibwe, Odawa and Potawatomi peoples. In particular, the university resides on land ceded in the 1819 Treaty of Saginaw.
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C.Y.T. and M.B.T. first conceived the project. C.Y.T. wrote the software for the Bayesian analysis. C.Y.T., M.B.T. and W.G.L. collected and evaluated all the constraints used in the analysis. R.K. researched, reviewed and validated the final set of constraints adopted in Table 1. R.K. also wrote some of the software codes used to analyse the Bayesian results and generated all the figures with data. C.J.H. contributed to the impact of the Urca cooling section. All authors contributed to the writing, editing and revising of the manuscript. The ordering of the authors reflects the length of time the authors have joined the project.
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Tsang, C.Y., Tsang, M.B., Lynch, W.G. et al. Determination of the equation of state from nuclear experiments and neutron star observations. Nat Astron 8, 328–336 (2024). https://doi.org/10.1038/s41550-023-02161-z
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DOI: https://doi.org/10.1038/s41550-023-02161-z
