Analyzed in detail a signal compatible with the much sought after ‘gravitational wave background’ (GWB), which astronomers have been chasing for some time: it would be a signal produced by the gravitational energy released by pairs of supermassive black holes during their reciprocal approach, which will eventually lead them to merge. Although it is not yet possible to confirm that the observed signal is really associated with the GWB, the study represents a step towards the detection of gravitational waves of very low frequency, of the order of one billionth of a Hertz, useful for better understanding the evolution. of the Universe. The results are published in the Monthly Notices of the Royal Astronomical Society by the EPTA (European Pulsar Timing Array) collaboration in which researchers from the National Institute of Astrophysics (INAF) and the University of Milano-Bicocca also participate.
The study was conducted by observing arrays of pulsars (very compact neutron stars that emit beams of radio waves) that with their ‘beacon effect’ are able to expand the observability window of gravitational waves. The data was collected over 24 years of observations with five large-aperture European radio telescopes, including the 64-meter-diameter Sardinia Radio Telescope (SRT), located near Cagliari.
“The presence of a gravitational wave background manifests itself in the form of very low frequency fluctuations in the rhythm of the radio pulses coming from all the pulsars, a sort of additional ‘noise’, which disturbs the regular trend of the pulses, which we could otherwise compare to ticking of a very precise clock ”, explains Andrea Possenti, researcher at the INAF of Cagliari and co-author of the work. “Speaking in a very simplified way, an experiment like the one conducted by EPTA therefore consists in the repeated observation of the array of pulsars, every few weeks and for many years, in search of a very low frequency ‘noise’ that afflicts their ticking in a common way. to all pulsars, and that it is not attributable to causes other than gravitational waves “.
Thanks to an elaborate analysis of the data collected during the observations, the EPTA researchers identified a clear signal potentially identifiable as belonging to the gravitational wave background. In particular, its spectral properties (ie how the amplitude of the observed ‘noise’ varies with its frequency) reflect theoretical expectations. “To confirm the nature of the signal we need to include more pulsar data in the analysis, but we can say that the current results are very encouraging,” comments Siyuan Chen, researcher at LPC2E, CNRS in Orleans, France, co-lead author. of study.
“As it was for high frequency gravitational waves in 2015, the detection of very low frequency gravitational waves would be an epochal achievement for physics, astrophysics and cosmology”, underlines Delphine Perrodin, researcher at INAF at Cagliari and co-author of the work. “In particular, the discovery and study of the gravitational wave background will give us direct information on the size and evolution of supermassive black holes, and on their contribution to modeling galaxies and the current universe.”
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Source From: Ansa
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