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Neutron star evolution with the Bemfica-Disconzi-Noronha-Kovtun viscous hydrodynamics framework

Harry L. H. Shum1,2, Fernando Abalos3,4, Yago Bea5, Miguel Bezares1,2, Pau Figueras6, and Carlos Palenzuela3,4

  • 1Nottingham Centre of Gravity, University of Nottingham, Nottingham NG7 2RD, United Kingdom
  • 2School of Mathematical Sciences, University of Nottingham, Nottingham, NG7 2RD, United Kingdom
  • 3Departament de Física, Universitat de les Illes Balears, Palma de Mallorca, E-07122, Spain
  • 4Institute of Applied Computing and Community Code (IAC3), Universitat de les Illes Balears, Palma de Mallorca, E-07122, Spain
  • 5Departament de Física Quàntica i Astrofísica and Institut de Ciències del Cosmos (ICC), Universitat de Barcelona, Martí i Franquès 1, ES-08028, Barcelona, Spain
  • 6School of Mathematical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom

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Phys. Rev. D 113, 084029 – Published 13 April, 2026

DOI: https://doi.org/10.1103/mthy-4119

Abstract

The recently proposed first-order viscous relativistic hydrodynamics formulation by Bemfica, Disconzi, Noronha, and Kovtun (commonly known as the BDNK formulation) has been shown to be causal, stable, strongly hyperbolic, and thus locally well posed. It is now a viable new option for modeling out-of-equilibrium effects in fluids, and has attracted wide attention in its potential applications to astrophysical systems. In this work, we present the first nonlinear numerical simulation of spherically symmetric neutron stars using the BDNK formulation under the Cowling approximation. Using a simplified equation of state, we show that stable evolutions can be constructed within a restricted parameter space up to the simulation time we explored. From these simulations, we analyze the frequency content of the quasinormal modes and the decay rate of the fundamental mode. This analysis serves as a first step toward constructing a fully consistent model of neutron stars using the BDNK formulation.

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Phys. Rev. D 113, 084029– Published 13 April, 2026
  • Received 30 September 2025
  • Accepted 16 March 2026
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