An Analytical Toy Equation of State for Neutron Stars Consistent with Current Observations
- 1Shanghai Jiao-Tong University
- 2Shanghai University
- 3Shanghai Key Laboratory of High Temperature Superconductors
Abstract
Fast analytic and semianalytic studies of neutron stars often require an equation of state (EOS) that is convenient to evaluate while producing relativistic stellar sequences compatible with current multimessenger constraints. We construct such a benchmark by scanning a smooth double-polytrope relation for the energy density as a function of pressure, ϵ ˆ ( p ˆ ) = a 1 p ˆ Γ 1 + a 2 p ˆ Γ 2 . The parameters are selected with filters based on massive pulsars, tidal deformability from the binary-neutron-star event GW170817, and NICER mass–radius measurements. A one-term baseline scan finds no model passing all filters, whereas a double-polytrope scan identifies a viable region. A curve-integral score, evaluated against public NICER and GW170817 posterior datasets, is then used to choose benchmark EOSs within this region. The selected benchmark EOSs support M max = 2.44 –2.49 M ⊙ , with R 1.4 ≃ 11.3 km and Λ 1.4 = 485–512, and remain causal on the stable branch. They exhibit superconformal sound-speed peaks with c s 2 / c 2 = 0.59 –0.71 at ϵ ≃ 452–471 MeV fm ⁻³ . This compact analytic family provides reference cases for relativistic stellar-structure tests at current observational scales.
Versions
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BibTeX
@article{chen2026analytical,
title = {{An Analytical Toy Equation of State for Neutron Stars Consistent with Current Observations}},
author = {Tian-Shun Chen and Xiao-Ding Zhou and Kilar Zhang},
journal = {The Astrophysical Journal},
year = {2026},
month = sep,
doi = {10.3847/1538-4357/aea217},
url = {https://iopscience.iop.org/article/10.3847/1538-4357/aea217},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - An Analytical Toy Equation of State for Neutron Stars Consistent with Current Observations
AU - Tian-Shun Chen
AU - Xiao-Ding Zhou
AU - Kilar Zhang
PY - 2026
DA - 2026/09/30
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/aea217
UR - https://iopscience.iop.org/article/10.3847/1538-4357/aea217
AB - Fast analytic and semianalytic studies of neutron stars often require an equation of state (EOS) that is convenient to evaluate while producing relativistic stellar sequences compatible with current multimessenger constraints. We construct such a benchmark by scanning a smooth double-polytrope relation for the energy density as a function of pressure, ϵ ˆ ( p ˆ ) = a 1 p ˆ Γ 1 + a 2 p ˆ Γ 2 . The parameters are selected with filters based on massive pulsars, tidal deformability from the binary-neutron-star event GW170817, and NICER mass–radius measurements. A one-term baseline scan finds no model passing all filters, whereas a double-polytrope scan identifies a viable region. A curve-integral score, evaluated against public NICER and GW170817 posterior datasets, is then used to choose benchmark EOSs within this region. The selected benchmark EOSs support M max = 2.44 –2.49 M ⊙ , with R 1.4 ≃ 11.3 km and Λ 1.4 = 485–512, and remain causal on the stable branch. They exhibit superconformal sound-speed peaks with c s 2 / c 2 = 0.59 –0.71 at ϵ ≃ 452–471 MeV fm ⁻³ . This compact analytic family provides reference cases for relativistic stellar-structure tests at current observational scales.
SN - 0004-637X
SN - 1538-4357
ER -