The Universe speaks to us: captured for the first time, thanks also to a team of Sardinian researchers, the background hum hypothesized by Einstein

An exceptional discovery which also bears the signature of researchers from the National Institute of Astrophysics (INAF) of Cagliari: astronomers have in fact announced that they have found evidence of a long-theorized form of gravitational waves which creates a " background hum " which it rumbles throughout the universe.

The breakthrough - achieved by hundreds of scientists using radio telescopes in North America, China, India, Australia, Europe and also in Sardinia, where the Sardinia Radio Telescope is operational - was hailed as a milestone that opens a new window on the universe .

The existence of these waves had been theorized by Albert Einstein but had never been proven so far.

Gravitational waves are ripples in the "fabric" of the universe that travel at the speed of light almost completely unhindered. Their existence wasn't confirmed until 2015, when US and Italian observers detected the first gravitational waves created by the collision of two black holes. These "high-frequency" waves were the result of a single violent event that sends a sharp, short, rippling blast toward Earth. But for decades, scientists have been searching for low-frequency gravitational waves, which are thought to be constantly moving through space as background noise. Joining forces under the banner of the International Pulsar Timing Array consortium, scientists working on gravitational-wave detectors on several continents have now revealed that they have finally found strong evidence for these background waves.

"We now know that the universe is flooded with gravitational waves," said Michael Keith, of the European Pulsar Timing Array .

To find evidence of this low-frequency pattern, astronomers looked at pulsars, the dead cores of stars that exploded in supernovae. Some rotate hundreds of times per second, flashing beams of radio waves at extremely regular intervals, like cosmic beacons. That means they can act like "a very, very accurate watch," Keith said.

THE STUDY - For the new research, radio telescopes from around the world were trained on a total of 115 pulsars across the Milky Way . The scientists then measured the incredibly small differences in the timing of the pulses, looking for the telltale signs of gravitational waves. The leading theory is that the waves come from pairs of massive black holes at the centers of slowly merging galaxies. Unlike those that have caused previously detected gravitational waves, these black holes are almost unimaginably large, sometimes billions of times larger than the Sun.

In the future, low-frequency gravitational waves could also reveal more about the Big Bang and possibly shed light on the mystery of dark matter , the scientists said, as well as gain a better understanding of how black holes and galaxies form and evolve.

THE ROLE OF SARDINIA – Europe has made an important contribution to the discovery of very low-frequency and ultra-long gravitational waves, with the European Pulsar Timing Array (EPTA) collaboration, and Italy, thanks to the National Institute of Astrophysics, with its headquarters in Cagliari and the University of Milan Bicocca. The result, published in several articles in the journal Astronomy and Astrophysics, is due to 13 telescopes from all over the world. Of these, 5 are European, including, in fact, the Sardinia Radio Telescope.

At INAF in Cagliari, the enthusiasm is palpable: «Thanks to EPTA's observations, we are opening a new window into the universe of ultra-long gravitational waves (corresponding to oscillation frequencies of one billionth of Hertz) which are associated with sources and phenomena unique», says researcher Caterina Tiburzi. My colleague Marta Burgay explains: «These gravitational waves allow us to study some of the hitherto unsolved mysteries in the evolution of the Universe, including, for example, the properties of the elusive cosmic population of binary systems formed by two supermassive black holes, having masses billion times greater than that of the Sun.

"It is a great satisfaction for all Italian astrophysics that the Sardinia Radio Telescope, the large radio telescope managed by INAF, is among the witnesses of the emergence in the data of this slow breath of space-time", explains Andrea Possenti , Senior Researcher of the INAF of Cagliari and one of the founders of EPTA together with the former president of the National Institute of Astrophysics Nichi D'Amico . And he specifies: «This is another great scientific result, which confirms, on a global level, the central role of Italy, and increasingly of Sardinia (with SRT and hopefully soon also with the Einstein Telescope), in the study of gravitational waves for many decades to come".

(Unioneonline/vl)