STROBE-X: Probing Neutron Star Structure and the Dense Matter Equation of State

The poorly understood behavior of matter at ultra-high densities, high proton/neutron number asymmetry, and low temperature presents one of the major outstanding problems in physics. Since matter in this extreme state only exists stably in the cores of neutron stars, astrophysical observations – of e.g. neutron star mass and radius - can provide key insight into the properties of matter in a region of the quantum chromodynamics phase space that is otherwise inaccessible. The proposed STROBE-X Probe-class mission, with its novel combination of large collecting area, superb spectral and temporal resolution, and rapid slew capabilities, will enable multiple complementary measurement approaches based on X-ray pulse profile modeling and spectroscopic techniques. Ultimately, STROBE-X is expected to deliver a high-quality data set that could lead to major progress towards definitive empirical constraints on the true nature of the densest matter in the Universe.