Scientists wonder about the origin of signals recorded in 2023
In 2023, astrophysicists discovered fluctuations in space-time, which baffled them. Scientists are still striving to find the source of the constant, albeit weak, «hum» gravitational waves that were discovered last year in the Milky Way. New research shows that these waves may have multiple sources.
The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) research group suggests that space-time fluctuations could result from the merger of supermassive black holes, each a billion times more massive than the Sun. If this hypothesis is correct, then further research will help determine the location and mass of these giant space objects.
However, Juan Urrutia from the National Institute of Physical Chemistry and Biophysics in Estonia notes that the presence of only one pair of black holes does not exclude the cosmological origin of the signals. His research showed that in addition to the black hole hypothesis, three other proposed cosmological sources could explain these data. This means that the gravitational signal may be the result of a mixed set of different sources.
Scientists note that this is a serious problem, since many signals are similar to each other. Exotic cosmological processes occurring in the early Universe include sources such as cosmic strings, phase transitions, and domain boundaries – high-energy phenomena. All of them may turn out to be one of the sources of gravitational wave signals.
It is especially interesting that domain boundaries arose immediately after the Big Bang, but before the spread of radiation throughout the Universe. Therefore, if the new results confirm the hypothesis about domain boundaries, then the detected signal will be the closest to the beginning of the Universe.
In addition, studies of phase transitions can also help in the search for dark matter and dark energy, which make up 95% of the Universe but remain invisible. Gravitational waves generated by the behavior of domain boundaries can contain large amounts of energy and lead to the formation of dark matter clusters.
When domain boundaries move and evolve, they contain large amounts of energy and emit gravitational waves. At some point they decay, from which clusters of dark matter are formed, — said Urrutia
This is especially interesting because these complex structures, which were proposed more than 50 years ago, may be an explanation for why there is more baryonic matter than antimatter in our Universe. Unlike baryonic matter, which is made up of positive protons and negative electrons, antimatter is made up of negative protons and positive electrons.
Since the Big Bang would have produced equal amounts of antimatter and baryonic matter, our Universe should, in theory, consist of equal amounts of both. In fact, baryonic matter completely predominates.
On the other hand, phase transitions provide scientists with the opportunity to study the various phases of development of the early Universe that created the baryon electrons, protons and neutrons we know. As with the boiling of water, cosmic phase transitions were caused by changes in the temperature of the Universe, where «bubbles» interacted with each other, creating gravitational waves similar to those recently discovered.
Detecting and identifying gravitational wave signals is a challenging task for astrophysicists, especially with the limited capabilities of existing telescopes. Currently, the LIGO Laser Gravitational Wave Interferometer is only capable of detecting high-frequency waves.
However, scientists are already preparing for the launch of the Laser Interferometric Space Antenna Complex LISA, — three-satellite network that will be capable of detecting lower-frequency waves like those recently discovered. LISA is scheduled to launch in 2037 and its measurement precision will be so high that it will be able to detect changes smaller than the diameter of a helium nucleus at a distance of a million miles.
In addition, the AEDGE dark matter and gravity experiment proposed in 2020 could help search for gravitational waves in frequency ranges between those that would be «audible» LISA and LIGO.
To achieve the promised accuracy of future detectors, however, it is necessary to have specific predictions and guidance for astrophysicists on what to look for and how to interpret the data, Urrutia notes: «The scientific community is making a huge effort to to ensure that calculations and guidance are as accurate as possible before launching these new experiments».