A new study proposes using next-generation gravitational-wave observatories to verify whether all neutron stars share a single equation of state. Currently, inferences about the equation of state (EOS) of dense matter inside these stars assume universality, meaning that a single EOS describes all neutron stars. However, the physics of dense matter under extreme conditions is poorly understood and could lead to distinct stellar subpopulations with different properties, invalidating this assumption.

Researchers have developed a framework based on hierarchical Bayesian inference and a piecewise-polytropic parametrization of the EOS. This method allows transforming the EOS universality from an assumption into a testable hypothesis. The study suggests that detecting approximately 30 to 50 binary neutron star mergers with a signal-to-noise ratio (SNR) above 100 by future observatories would be sufficient to detect deviations from universality.

Even if only 10% or 20% of the neutron star population exhibits one of the non-universality parametrizations considered, these gravitational-wave observations could provide compelling evidence. This would open a new window for understanding the composition and behavior of the densest matter in the universe, challenging current theories about the internal structure and evolution of neutron stars.