M. Kramer

The night sky looks calm, but if you listen in on the radio band, it's full of short clicks and rustles. Astronomers are combing the sky for solitary radio pulses — bursts lasting milliseconds that come from various corners of the Galaxy and beyond. One such search is underway at the 100-meter radio telescope in Effelsberg, Germany.

A lighthouse flashes for a fraction of a second and goes dark again. The MeerKAT telescope in South Africa catches such flashes in the radio band. During its observations, it picked up 27 new sources that no one had seen before. Neutron stars are the remnants of exploded stars, compressed to the size of a city.

It's like a sprint record: to break it, you need a perfect run-up. But for sub-millisecond pulsars, the run-up is too short. The fastest known pulsar, PSR J1748-2446ad, spins 716 times per second — faster than a kitchen blender. If it were the size of Earth, a point on its equator would move at about 0.24 times the speed of light. But why doesn't any pulsar spin even faster?