In 1181, in the constellation Cassiopeia, a "guest star" blazed into view — a bright spot that rivaled other luminaries for half a year. Most likely, it was the merger of two white dwarfs, the burned-out remnants of stars like our Sun. What remains is nebula Pa 30: a cloud of tenuous gas and cosmic dust, expanding at a breakneck pace — nearly 5% the speed of light. Yet modern radio telescopes pick up only a faint whisper instead of the expected roar.

Typically, a supernova's shockwave accelerates charged particles to near-light speeds, making them "scream" in radio waves. Pa 30 is silent — its radio emission is a thousand times weaker than that of the Crab Nebula with a neutron star inside. This means either the explosion was surprisingly sluggish, or particle acceleration works differently. It’s precisely this scenario — a white dwarf merger without a powerful radio echo — that Subrahmanyan Chandrasekhar predicted back in the 1930s while studying the mass limit of these objects.

The most unexpected conclusion: our Galaxy may be littered with dozens of such invisible ghosts. We simply hadn't noticed them, and now we’ll have to rewrite the history of stellar explosions in the Milky Way.