Somewhere in the depths of space, two supermassive black holes are circling each other. Their dance is not smooth — the orbit is stretched, like a rubber band that alternately tightens and relaxes. Each revolution sends ripples through the fabric of spacetime — gravitational waves. They spread in all directions and, millions of years later, reach Earth, stretching and squeezing it by less than the size of an atomic nucleus.

Astronomers are trying to catch this whisper using networks of radio telescopes — pulsar timing arrays. They monitor dozens of pulsars (rapidly spinning neutron stars whose pulses arrive like clockwork). If a gravitational wave passes between a pulsar and Earth, the rhythm is disrupted. The main prize is a continuous signal from a single pair of black holes, especially if their orbit is far from a perfect circle. In the new study, scientists tested how such a signal could be picked out from the background noise created by hundreds of thousands of distant binary systems.

It turns out that at high frequencies, when the black holes whiz close to each other, their individual masses can be measured quite accurately. This is like weighing two rapidly spinning tops by the whistle they emit. But at low frequencies, the signal is almost indistinguishable from the background, like trying to make out one singer's voice in a huge choir. The authors wrote a program that runs on graphics cards and speeds up complex calculations. This will allow faster processing of real data in the future and, possibly, the first detection of such an eccentric pair.