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Rhythmic flashes of a lighthouse in thick fog: that's what searching for pulsars looks like. The lighthouse spins, and its beam periodically sweeps across the telescope. But the fog smears the light, making the period seem slightly different. If the same lighthouse was observed twice, you can compare: the periods should nearly match, and the smearing should be similar. That's exactly how the new algorithm for finding pulsars, rapidly rotating neutron stars that emit radio pulses, works.

A pulsar is a neutron star left behind after a supernova explosion. It rotates, and its radio beam, like a lighthouse beam, periodically sweeps past Earth. But between us and the pulsar lies interstellar gas, which slows radio waves: lower frequencies arrive later than higher ones. This "smearing" is called the dispersion measure. The algorithm compares two quantities for candidates: the rotation period (should match within 1%) and the dispersion measure (within 10%). If both conditions are met in different observations of the same sky region, it's the same pulsar.

The method was tested on data from the FAST telescope (the five-hundred-meter radio telescope in China). In the observation archive of the globular cluster M12, two candidates were found that had not been linked before. It turned out they are one pulsar — named M12B. It rotates once every 2.76 milliseconds — faster than a kitchen blender. Its signal is faint, flickers (like stars due to air turbulence), and has three peaks per period. The pulsar is in a binary system: it orbits a companion every 0.53 days.

This approach is like going through old photographs and spotting the same person in them. It doesn't require new telescope time; it uses what's already been accumulated. If the algorithm is applied to archives of other globular clusters, many more pulsars hiding in the noise could be found.