A soup of subatomic particles can start spinning wildly just because a magnetic field was turned on.
The Einstein-de Haas effect has been identified in hot nuclear matter for the first time. This effect causes magnetic-field-induced spin alignment to translate into physical, collective rotation of the entire particle fluid. High-energy collisions in particle accelerators usually require an initial 'swirl' to create rotation. This discovery shows that the magnetic field alone can generate the spin from nothing. This insight helps physicists understand the extreme conditions inside neutron stars and the very early universe. It reveals a powerful new way that magnetic fields can shape the movement of matter at the subatomic level.
Einstein-de Haas effect and induced rotation in QCD matter
arXiv · 2605.03093
In this study, we report the first identification of the Einstein-de Haas (EdH) effect in the QCD matter. The EdH effect is a fundamental magnetomechanical coupling wherein magnetic-field-induced spin alignment generates a compensating collective rotation to conserve the total angular momentum. Using an equilibrium hadron gas under an external magnetic field, we show that even remnant magnetic fields at the freeze-out produce induced rotations ($\omega_{\mathrm{EdH}}$) comparable to typical esti