A magnetar's crust cracks in milliseconds. A deep shift generates seismic waves that run across the surface and shake the magnetic field. This starquake is like an earthquake, but on a neutron star with a field a quadrillion times stronger than Earth's.

Until now, models of perturbations were crude: a single rotation of the surface or an idealized pulse. No one knew how the complex spectrum of crustal oscillations transfers energy to the magnetosphere. The authors of the new study performed a two-step calculation. First, they solved the magnetoelastic equations for a crust 860 meters thick and obtained oscillations with a frequency of about 1 kHz. Then these surface motions served as the boundary condition for a three-dimensional simulation of the magnetosphere in force-free electrodynamics, where the plasma is massless and the field dominates.

The waves start linear with an amplitude of about 0.01 of the background field. But as they propagate outward in the decaying dipole field, they amplify: Alfvén waves grow as (r/r∗)^(3/2), and fast magnetosonic waves as (r/r∗)^2. Nonlinearity sets in at radii of 10–20 stellar radii. Alfvén waves open closed magnetic loops, forming nonlinear ejections and equatorial current sheets where reconnection occurs. Fast magnetosonic waves form 'monster shocks,' structures with relativistic drift velocities (γv/c up to 10). The energy balance is surprising: only 7±2% of the Alfvén wave energy escapes outward as nonlinear ejections, 52±5% remains trapped in closed loops, and fast waves carry up to 44±4% of the total perturbation energy. After t=100 r∗/c, the magnetosphere is strongly distorted and transitions to a partially split monopole configuration.

The result changes the picture. Previously, it was thought that Alfvén ejections efficiently carry away energy and trigger fast radio bursts. Now it is clear that their contribution is an order of magnitude lower than predicted by single-pulse models. Most of the energy is spent on deforming the background field. The main energy carriers turn out to be fast magnetosonic waves and monster shocks. This places tight constraints on FRB mechanisms based on Alfvén ejections and shifts the focus toward other scenarios.

A starquake on a magnetar is not just a jolt. It is a conductor that makes the entire magnetosphere resonate at the crust's frequency. And now we hear this music in the quasi-periodic oscillations of radio bursts.