The Nobel Prize-winning detection of gravitational waves added a new observational tool for astronomers to use in studying celestial events. But an as-yet-unobserved phenomenon would make all the gravitational wave detections so far seem like small potatoes.

When two galaxies merge, the supermassive black holes at their centers would merge as well, and the process would emit gravitational waves. But the wavelength of those waves would be undetectable by the LIGO observatory. They're best detected by pulsar.

Pulsars emit electromagnetic radiation at regular intervals. A gravitational wave would slightly change the distance from the Earth to a pulsar, and thus slightly change the pulsar's timing as well.

In a paper in Nature Astronomy, astronomers use observation data and models of supermassive black hole merger events to conclude that we should be able to detect such an event within the next 10 years. If we don't, it could indicate that our hypotheses about these large black hole mergers need some refinement.