When a massive star explodes as a supernova, its core collapses into a neutron star the size of a city. Spinning and sending out radio pulses, it becomes a pulsar — objects discovered in 1967 by Jocelyn Bell Burnell and predicted earlier by Fritz Zwicky.

Sometimes a pulsar gets a kick and shoots out beyond the supernova remnant — a cloud of gas. It plows into the thin interstellar medium like a motorboat: a shock wave generates a glowing tail. "Thunder" is this tail inside the "Nimbus" shell, shining in radio waves. Polarimetry measurements (the alignment of waves) revealed that the magnetic field is stretched along the direction of motion. The field accelerates plasma particles to near light speed — that's how cosmic rays are born. The field is a hundred thousand times weaker than a fridge magnet, yet stretches across light-years. The pulsar itself races so fast it could cover the Earth-Moon distance in a minute.

The system's age is 30,000–45,000 years. It shows how neutron stars leave their 'cradles', dispersing energy. New telescopes will watch the tail change, just like a boat's wake in fog.