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Event details

Title: Self-Gravitating Anisotropic Fluids

Abstract:��Fluid anisotropies are a well-studied mechanism thought to have significant effects on the structure of self-gravitating bodies. In the application of neutron stars, it was conjectured that the strong nuclear force may act as a source for additional anisotropic stresses. However, the historical development of self-gravitating anisotropic bodies in general relativity often relied on ad hoc definitions which frequently violated the weak equivalent principle and lacked microphysical motivation. In this presentation I will present my recent work with Eric Poisson (2406.03185, 2406.03191, 2406.03196) on a fully covariant theory of anisotropic fluids, in Newtonian and relativistic gravity, inspired by the study of liquid crystals. In this, a dynamical “director” field is introduced to characterize the local structure of the fluid, and whose gradients generates the anisotropic stress. I will then discuss the application of the theory to a polytropic stellar model, wherein we find that spherical anisotropic fluids should not be expected to exist in isolation. We remedy this by partitioning the body into an anisotropic core and isotropic outer shell. Finally, the effects of the anisotropy on the density and mass profiles as well as the stellar mass-radius curves will be discussed, from which we conclude that anisotropic bodies are generally less compact than their isotropic counterparts, contrary to the historical literature.