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 state the presence of a point source of background 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 calmest place, here stars explode, supermassive black holes merge and neutron stars collide. Such phenomena cause gravitational waves, which scientists first registered 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, the gravitational ripples that arise in space can be observed using indirect measurements. In particular, millisecond pulsars can be used - rotating neutron stars that emit radio pulses with a constant period of one to ten milliseconds. The stability of the rotation of a millisecond pulsar allows scientists to build accurate time models that take into account both its internal and external physics, and the most accurate models are able to predict the pulse arrival time with an accuracy of tens of nanoseconds. Distortions in space-time caused by gravitational waves cause correlations between the difference in the arrival of signals from pulsars and the expected signal arrival time calculated by the models. Scientists have already used these correlations to observe the background of gravitational waves, for example in the NANOGrav experiment, however, it took about 15 years to collect sufficient statistics, and the first reliable results were published only last year.
Now the MeerKAT collaboration has provided evidence of the existence of the gravitational wave background based on data collected over just four and a half years. The astrophysicists used the MeerKAT radio telescope 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 one array.
Scientists used the arrival times of signals from 83 pulsars and collected statistics of 250,000 events with an average error of only about three microseconds. As a result of the data analysis, astrophysicists confirmed the existence of a gravitational wave background and compiled a map of it in the frequency range from 7 to 21 nanohertz. Scientists see a hot spot with a p-value of 0.015 on this map, but in their opinion, the statistical significance is not yet sufficient to reliably state the presence of a single source of the background. In addition, as scientists note, the p-value may overestimate the value of anisotropy due to underestimation of cosmic dispersion.
Scientists continue to study the background of gravitational waves by observing pulsars. You can read about how else gravitational waves can be used to study the Universe in our article “Behind the Wave, the Wave.”
