Maximum possible mass of a non-spinning neutron star

Determine the maximum possible gravitational mass of a non-spinning neutron star, using constraints from terrestrial nuclear experiments, electromagnetic observations of neutron stars, and gravitational-wave measurements, to sharpen the classification of compact binary coalescence sources into binary black holes, neutron star–black holes, and binary neutron stars.

Background

In classifying compact binary coalescence sources, the component masses are crucial for distinguishing between black holes and neutron stars. The catalog notes that the maximum non-spinning neutron star mass is uncertain, which directly affects whether a given component can be confidently labeled as a black hole or a neutron star.

Although multiple lines of evidence—from nuclear physics, pulsar timing, x-ray observations, and gravitational-wave detections—have constrained this maximum mass to a range of roughly 2.2–2.5 solar masses, the paper adopts a conservative upper limit of 3 solar masses for classification. A definitive determination would reduce ambiguity in source typing across the catalog and improve population and astrophysical inferences.

References

The maximum possible non-spinning NS mass is unknown, although data from terrestrial experiments, electromagnetic observations of NSs, and GW detections have been used to bound this mass to ~ 2.2–2.5 Mo.

— GWTC-4.0: Updating the Gravitational-Wave Transient Catalog with Observations from the First Part of the Fourth LIGO-Virgo-KAGRA Observing Run (2508.18082 - Collaboration et al., 25 Aug 2025) in Section 3.1 (Masses)