Next-generation gravitational wave detectors, Einstein Telescope and Cosmic Explorer, will observe thousands of binary neutron star mergers and offer unprecedented precision on neutron star parameters. But precision without accuracy is a problem. Systematic biases in waveform models, prior assumptions, and pipeline choices can lead to confident but wrong measurements.

This paper gives a comprehensive assessment of how accurately next-generation detectors can measure neutron star radii, identifying and quantifying the dominant sources of systematic error. We show that achieving sub-percent accuracy on the radius, a key target for constraining the equation of state, requires careful control of waveform systematics and prior choices, and we give practical recommendations for the O5 era and beyond.

Published in Physical Review D (2025)