Elena D'Onghia

A galactic disk is like a frozen ripple on water: every disturbance leaves a trace that can be read billions of years later. When a dwarf satellite galaxy flies past or a head-on merger occurs, stars in the disk start to oscillate, like bobbers rocked by a wave.

At the center of the Large Magellanic Cloud, the massive dwarf galaxy nearest to us, the conductor is invisible. Astronomers have long suspected that a supermassive black hole is hiding there, but telescopes catch no radiation from it. It is as if an orchestra were playing without a baton: stars whirl, gas glows, and the source of gravity directing this dance stays in the shadows.