South Africa’s already-renowned MeerKAT radio telescope array, located in the Karoo region in the Northern Cape province, has been the key means of making yet another major scientific breakthrough. In this latest triumph, data from MeerKAT allowed an international team of South African, Australian and European astronomers to detect “compelling evidence” for what is called the low-frequency gravitational wave background.

(The South African team members were from the University of Cape Town (UCT) and the South African Radio Astronomy Observatory (SARAO). SARAO developed and operates MeerKAT, under the aegis of the National Research Foundation.)

The low-frequency gravitational wave background are ripples in cosmic spacetime that stretch and squeeze the very fabric of the universe. Gathering evidence for them requires observations stretching over multiple years. The MeerKAT gathered the necessary data in record time – less than 33% of the time previously required.

Gathering the data involved very precise observations of a network of pulsars. These are rapidly spinning neutron stars (which are incredibly dense bodies, resulting from the collapse of normal stars after they ran out of their sources of nuclear energy), thousands of light years from Earth, which emitted radio or X-ray energy with incredible preciseness. This made them invaluable “cosmic clocks”.

“To find evidence for a gravitational wave background, we first need to model the timing behaviour of each of the pulsars in our network very precisely,” pointed out UCT lecturer, study co-author and former MeerKAT commissioning scientist Dr Marisa Geyer. “Once we know the individual pulsars well, we can start analysing the combined behaviour of the group of pulsars. If we see pulsars in the same direction in the sky lose time in a connected way, we start suspecting that it is not the pulsars that are acting funny, but rather a gravitational wave background that has interfered.”

The experiment was designated the MeerKAT Pulsar Timing Array project. It was launched in 2019.

“Pulsar timing array experiments are long term in nature and searching for a gravitational wave background is a slow process,” explained UCT postdoctoral fellow Dr Jaikhomba Singha. “From past experience, we know that this may need 15 years of data. It is amazing to see that, with MeerKAT, evidence of the signal is possible even in a data-span of just 4.5 years..”

“We have achieved fantastic pulsar sensitivity and timing precision with MeerKAT,” enthused SARAO Science Operations lead Sarah Buchner. “It is deeply moving to see the exquisite results from the Pulsar Timing Array project.”