Listening to the long ringdown: A novel way to pinpoint the EOS in neutron-star cores

Christian Ecker; Tyler Gorda; Aleksi Kurkela; Luciano Rezzolla

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arXiv · 2509.18665

Listening to the long ringdown: A novel way to pinpoint the EOS in neutron-star cores

Christian Ecker·Tyler Gorda·Aleksi Kurkela·Luciano Rezzolla

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Abstract

Gravitational waves (GWs) from binary neutron star (BNS) merger remnants complement constraints from the inspiral phase, mass-radius measurements, and microscopic theory by providing information about the neutron-star equation of state (EOS) at extreme densities. We perform general-relativistic simulations of BNS mergers using EOS models that span the uncertain high-density regime. We find a robust correlation between the ratio of energy and angular momentum lost during the late-time post-merger GW signal - the long ringdown - and the EOS at the highest densities in neutron star cores. Applying this correlation to post-merger GW signals reduces EOS uncertainty at several times saturation density, where no direct constraints currently exist.

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Christian Ecker, Tyler Gorda, Aleksi Kurkela, Luciano Rezzolla. 2025-09-23. Listening to the long ringdown: A novel way to pinpoint the EOS in neutron-star cores. https://arxiv.org/abs/2509.18665

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