Galaxy TXS 0506+056 is an active galactic nucleus with a supermassive black hole at its centre, surrounded by a swirling disk of gas. From the poles erupts a jet of superheated plasma, shooting almost directly at Earth. Due to the expansion of the Universe, its light has been redshifted — an effect first described by Maarten Schmidt. In 2017, a neutrino arrived with the punch of a hockey puck, but observations from the VLBI network showed the jet crawling at just 1–2 times the speed of light — way too slow for such a neutrino.

Re-analysing 15 years of radio data, scientists stopped tracking individual blobs and noticed a hidden wave zipping along at an apparent speed of 21 times the speed of light — this superluminal trick arises from the laws of relativity of Einstein and Lorentz. The jet works like a nesting doll: inside lurks an invisible high-speed spine, and wrapped around it is a sluggish outer shell. The neutrino is born in the spine instantly, but the radio flare only becomes apparent years later, when the shock wave hits the shell and snaps the magnetic field lines back together. In 2021, the pattern repeated — meaning nesting-doll jets are everywhere.