Pressure of neutron-star matter between two and eight times nuclear density
In plain words
How hard dense matter pushes back sets how large a neutron star of a given mass is. The goal is to pin down this pressure from star observations combined with theory.
Precise statement
Determine the pressure $P(n)$ of cold beta-equilibrated matter for baryon density n between $2\,n_0$ and $8\,n_0$ ($n_0 = 0.16\,\mathrm{fm}^{-3}$) with 10 percent uncertainty, combining chiral EFT below about $2\,n_0$, perturbative QCD above about $40\,n_0$, pulsar masses, NICER (X-ray timing telescope) radii and gravitational-wave tidal deformabilities. Answer: a $P(n)$ band with stated priors.
What would settle it
Radius measurements with 2 percent precision for stars of 1.4 and 2.0 solar masses, together with post-merger gravitational-wave spectra from next-generation detectors.
Status in the literature
Unverified note
Combined analyses since 2018 constrain the radius of a 1.4 solar-mass star to roughly 1.15e6 to 1.3e6 cm, while the pressure above about $3 n_{0}$ remained weakly constrained as of 2026.