Gamma rays from pulsars could help detect merging supermassive black holes.

Researchers have found a new way to look for gravitational waves and ripples in space-time, which are due to explosions, rotations or mergers of massive celestial objects.

Physicists first detected gravitational waves in 2015 using laser detectors, and they were also recorded by ground-based radio telescopes. Now, new work shows that gravitational waves can be searched for with the Fermi Gamma Ray Space Telescope. So far, this method is not accurate enough, but it helps other researchers refine their observations.

Today, radio astronomers are looking for mega-mergers that occur between supermassive black holes, each weighing billions of suns. Such black holes hide in the centers of galaxies.

When two galaxies merge, the black holes are thought to orbit close to each other and slowly approach each other. Ordinary telescopes will not be able to detect such an event, so you need to track gravitational waves and do it in different ways.

The authors of the new work proposed to use pulsars – these are neutron stars that emit radiation from their poles. When they rotate, the radiation sweeps across the sky like a beacon beam. On Earth, astronomers see some pulsars flash hundreds of times per second. A passing gravitational wave will slightly change the distance between the pulsar and the Earth. Therefore, the authors proposed to track the arrival time of pulses from many pulsars throughout the Milky Way over many years. This is how astronomers hope to detect small changes that signal gravitational waves.