Original title: Vortex pinning and the elastic response of neutron-star crusts II. Non-axisymmetric loading and Magnus mountains
Elia Giliberti · September 2026
Neutron stars are dead stars that pack immense mass into a tiny space. Inside them, rotating superfluidA state of matter that flows with zero viscosity, like certain quantum fluids. swirls in tiny whirlpools called vorticesTiny, stable swirls in a superfluid that carry angular momentum.. When these vortices stick, or pin, to the solid outer crust, they push against it with a sideways force called the Magnus forceA sideways force on a spinning object moving through a fluid, caused by pressure differences.. If this push is uneven, it can squeeze the star out of shape and create a lasting bulge, known as a mass quadrupoleA measure of asymmetry in mass distribution, indicating a bulge or deformation. or mountain. Researchers modeled this squeezing in stars using two different interior models, SLy4 and BSk21. For a 1.4 M_sun star spinning at 100 Hz, the maximum uneven shapes reached epsilon=2.67x10^-9 for SLy4 and 2.44x10^-9 for BSk21. They discovered that the crust's resistance to shear matters very little. Instead, how the deep inner crust compresses under pressure controls how large these mountains grow.
Imagine you're spinning a wet tennis ball and tossing it through the air. As it spins, the air resistance might cause it to wobble or develop a slight bulge because of how it interacts with the air. Here, in a neutron star, the swirling matter is like the spinning ball, and it pushes on the solid outer layer to create a tiny permanent bulge that depends mainly on how the deep layers compress.
This affects how we interpret signals from neutron stars, like gravitational waves, because the bulges change the star's shape and how it radiates energy.
The abstract does not provide a comprehensive analysis of all neutron star models or uncertainties. It notes that their calculation uses a specific benchmark and that their results are more than an order of magnitude below a previous cylindrical calculation, indicating that more ingredients might be required for a complete model.
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Vortex pinning and the elastic response of neutron-star crusts II. Non-axisymmetric loading and Magnus mountains — Elia Giliberti
Abstract licence: CC0
Explanation generated by Synthesis from the abstract — it is not the original paper. This is a preprint, so it hasn't necessarily been peer reviewed.