Globular clusters, dense swarms of hundreds of thousands of stars, hide millisecond pulsars. These are dead stars spinning at breakneck speed: one rotation every few milliseconds, like a kitchen blender on max. Their radio pulses arrive at Earth with clock-like precision, but the signal is so faint that in a standard search it drowns in noise, like a whisper in a crowd.

Astronomers have found a way to hear that whisper. They took data from the FAST radio telescope (a five-hundred-meter dish in China's Guizhou province) and stacked power spectra from many observations of the same patch of sky. The stacking amplified weak periodic signals, and in two globular clusters — NGC 6517 and M15—six new pulsars emerged. Four are in NGC 6517, two in M15.

All six pulsars have rotation periods from 3.68 to 9.28 milliseconds. For comparison, a typical spinning top makes a turn in fractions of a second, but here a whole star with the mass of the Sun spins hundreds of times faster. Three of the new pulsars (M15N, NGC 6517U, and NGC 6517V) would have been missed by standard search methods. Only the new stacking technique found them.

So far, a precise rotation model has been built for only one pulsar — M15M. The others are seen too rarely to link their pulses into a single chain. But it's already clear: all six are loners, without companion stars. This is expected in globular clusters, where stars often collide and break up pairs.