The night sky is full of beacons that blink on schedule. Pulsars are fast-spinning neutron stars whose radio pulses arrive with clockwork precision. But there are other beacons too: they stay silent for minutes or hours, then suddenly emit a single pulse, and go quiet again. These objects are called rotating radio transients, and until now they were thought to be a rare curiosity.
This new study combines data from four sky surveys conducted with the Parkes radio telescope in Australia. The astronomers assembled a catalog of 335 such 'quiet ones' and built a model of their population in the Galaxy. It turns out there are about 34,000 bright radio transients that our telescopes could detect — about the same as the number of ordinary pulsars. But unlike pulsars, these stars spin more slowly: their periods are noticeably longer. This hints that radio transients are older, 'tired' relatives of pulsars that lose stability over time.
Such numbers don't require any special birth history. According to the authors' estimates, new radio transients appear no more often than 1.4 times per century — which matches the rate of supernova explosions that give birth to neutron stars. So radio transients are not a separate exotic species but a natural stage in the life of many pulsars. Future sky surveys, such as the SKA, will be able to test these predictions and find thousands of new 'silent beacons.'
The first rotating radio transient was discovered in 2006 by accident: an algorithm was searching for periodic signals and discarding single bursts, but one of them was too bright to ignore.