By studying the light emitted from the very dense and strongly magnetic neutron star RX J1856.5-3754, a team of astronomers has found the strongest observational indications yet of vacuum birefringence, a strange quantum effect first predicted nearly 80 years ago. Color composite photo of the sky field around RX J1856.5-3754 and the related cone-shaped nebula. RX J1856.5-3754 is exactly in the centre of the image. The trail of an asteroid is seen...