Relativistic Bulk Rheology: From Neutron Star Mergers to Viscous Cosmology

TL;DR

This paper introduces the first causal and stable relativistic bulk-viscous pseudoplastic fluid theory, revealing rheological behaviors in neutron star mergers, relativistic plasmas, and cosmological models with pseudoplastic or dilatant properties.

Contribution

It develops a novel formalism for a causal, stable relativistic pseudoplastic fluid applicable to astrophysical and cosmological systems.

Findings

Neutron star collisions exhibit pseudoplastic viscous behavior.

Relativistic plasmas around black holes are predominantly pseudoplastic.

The framework enables new viscous cosmological models with dilatant features.

Abstract

We develop the first causal and stable theory of a bulk-viscous relativistic pseudoplastic (or dilatant) fluid. This new formalism brings to light the rheological properties of several relativistic physical systems. Neutron star collisions can behave as a relativistic pseudoplastic material with viscous properties dictated by the non-conservation of lepton currents due to weak decay. Two-temperature relativistic plasmas, such as those surrounding supermassive galactic black holes, are predominantly pseudoplastic. Our framework can also be employed to construct novel viscous models for the evolution of the Universe with pseudoplastic or dilatant features.