Astrophysicists from the MeerKAT collaboration have confirmed the existence of a gravitational wave background in the Universe. To do this, the scientists used the MeerKAT radio telescope, which consists of 64 antennas. Although the physicists see a hot spot on the background map obtained during data processing, the statistical significance of the observation is not yet sufficient to reliably confirm the presence of a point source of gravitational waves. The scientists presented their results in a series of papers [1, 2, 3] recently published on the preprint website arXiv.org.
Our Universe is not the most tranquil place: stars explode, supermassive black holes merge, and neutron stars collide. These phenomena produce gravitational waves, which scientists first detected only in 2016. You can read more about gravitational waves in our article "On the Crest of the Metric Tensor."
In addition to direct observation, gravitational ripples in space can be observed through indirect measurements. In particular, millisecond pulsars—rotating neutron stars that emit radio pulses with a constant period of one to ten milliseconds—can be used. The rotational stability of a millisecond pulsar allows scientists to construct precise timing models that take into account both its internal and external physics, with the most accurate models capable of predicting pulse arrival times with an accuracy of tens of nanoseconds. Distortions in spacetime caused by gravitational waves produce correlations between the delay in signal arrival times from pulsars and the expected signal arrival times calculated by the models. Scientists have already used these correlations to observe the gravitational wave background, for example in the NANOGrav experiment. However, it took about 15 years to accumulate sufficient data, and the first reliable results were published only last year.
Now, the MeerKAT collaboration has confirmed the existence of a gravitational wave background based on data collected over just four and a half years. The astrophysicists used the MeerKAT radio telescope, located in South Africa—the largest and most sensitive radio telescope in the southern hemisphere. The telescope consists of 64 individual radio antennas, each 13.5 meters in diameter, combined into a single array.
Scientists used the arrival times of signals from 83 pulsars and collected statistics on 250,000 events with an average error of only about three microseconds. After analyzing the data, the astrophysicists confirmed the existence of a gravitational wave background and mapped it in the frequency range from 7 to 21 nanohertz. The scientists see a hot spot on this map with a p-value of 0.015, but they believe the statistical significance is not yet sufficient to reliably confirm the presence of a specific background source. Furthermore, the scientists note that the p-value may overestimate the anisotropy due to underestimation of cosmic dispersion.
Scientists continue to study the gravitational wave background by observing pulsars. You can read about other ways gravitational waves can be used to explore the universe in our article "Behind the Wave."
