In the galaxy NGC 3627, a trail of cosmic dust and gas has been found, resembling the wake of a speedboat. The role of the speedboat was played by a massive black hole or the core of a dwarf galaxy that tore through the disk at over 300 km/s. The wake stretches for 26,000 light-years but is just 650 light-years wide — like a pencil line drawn across a football field. The gas inside moves chaotically at tens of kilometers per second, hinting at a recent event: only about 20 million years ago.

The object that left this trail likely had a mass millions of times that of the Sun — an invisible giant that gave itself away by rippling the galactic disk. Such wakes can be spotted by telescopes like James Webb and ALMA, opening a new way to hunt for hidden massive bodies.