Some stars don't vanish after they die; instead, they turn into tiny, superdense spheres about the size of a city. These spheres spin very fast and send radio signals into space, like lighthouses. Such stars are called pulsars. But over time, their spin slows down, and according to old calculations, a pulsar should go silent. Yet it doesn't. Why?

It turns out that around a pulsar, there's an invisible cloud of particles that scientists call axions. These particles haven't been detected yet, but they could exist and influence the star. The cloud acts like an invisible conductor: it doesn't touch the instruments, but it changes the music. In one place, it helps particles speed up; in another, it hinders them. And this allows the pulsar to keep shining even when it shouldn't.

Scientists tested this on a computer. They slowed the star's rotation by a factor of four and saw that the cloud still maintained the glow. This means that old pulsars can live longer than we thought. And it provides a new way to search for invisible particles: by observing pulsars, we can tell whether such a cloud surrounds them.