Crustal Failure Stresses in Magnetars: Surface Magnetic Stress Against the Breaking Strength of the Neutron Star Crust

A magnetar crust is a Coulomb crystal a kilometre thick, threaded by the strongest magnetic fields known. The field pushes on the crust with a stress that grows as the square of its strength, and the crust answers with a finite breaking strength set by its shear modulus and the strain it can tolerate before it yields. Where the two curves cross, the surface must give way. Working from published values for the sources concerned, this paper computes the relevant quantities under one stated set of conventions and compares them source by source. Headline results: breaking field theta0.01 G 5.01e+14; breaking field theta0.1 G 1.59e+15; sources surface stress above theta0.01 3; highest stress source SGR 1806-20; highest stress dyn cm2 1.51e+29. The comparisons are budget statements: they establish whether the energies, stresses, powers and timescales involved are mutually consistent, and by what margin. Every number quoted is produced by the deposited compute.py script from the stated inputs, and the full per-source record is deposited as results.json alongside the text.