Thermonuclear explosions on neutron stars reveal the speed of their jets.

Relativistic jets are observed from accreting and cataclysmic transients throughout the Universe, and have a profound impact on their surroundings. Despite their importance, their launch mechanism is not known. For accreting neutron stars, the speed of their compact jets can reveal whether the jets are powered by magnetic fields anchored in the accretion flow or in the star itself, but so far no such measurements exist.