An ordinary white dwarf holds itself together against gravity thanks to the quantum pressure of electrons. This pressure acts like a spring: pushing equally in all directions. But when you switch on an ultra-strong magnetic field, electrons start to spiral along field lines — a discovery by Lev Landau. Motion across the field becomes quantized, and the spring stiffens in one direction while softening in another. An anisotropy emerges: pressure along the field is greater than across it. The star gets squeezed by an invisible magnetic corset.

Physicists modeled this effect by adding directional pressure to the equilibrium equations. They accounted for how the core's composition changes at colossal densities and ran a numerical simulation. The result: a typical dwarf's radius shrinks by tens of kilometers, while the maximum possible mass remains almost unchanged. The limit found by Subrahmanyan Chandrasekhar held firm. Why? At the center, where density peaks, so many quantum levels are filled that the anisotropy smooths out.

Now astronomers can more accurately determine radii of magnetic dwarfs, comparing models with observations. The magnetic corset does not break the established theory, but adds a subtle detail that explains the compactness of some objects.