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After 25 years of observations, an international team of astronomers have seen the first evidence of ultra-low-frequency gravitational waves.

The waves are expected to come from pairs of supermassive black holes found in the centres of merging galaxies and the discovery could hold answers about the formation and evolution of the Universe and the galaxies that populate it, including our own Milky Way.

The finding stems from observations made over the last 25 years using six of the world's most sensitive radio telescopes, including the Lovell Telescope at The University of Manchester鈥檚 Jodrell Bank Observatory, and is presented by a team of researchers from the European Pulsar Timing Array (EPTA), in collaboration with Indian and Japanese colleagues of the Indian Pulsar Timing Array (InPTA).

The results are published today in the journal Astronomy and Astrophysics.

Dr Michael Keith, Lecturer at Jodrell Bank Centre for Astrophysics at the University of Manchester, said: 鈥淭he results presented today mark the beginning of a new journey into the Universe to unveil some of its unsolved mysteries.

"We are incredibly excited that after decades of work by hundreds of astronomers and physicists around the world, we are finally seeing the signature of gravitational waves from the distant Universe.鈥�

Gravitational waves are ripples in space that can be produced by two objects orbiting each other. But they are extremely weak and hard to detect.

The observation of gravitational waves produced by orbiting pairs of supermassive black holes, which are hundreds of millions of times the mass of our sun, will allow us to learn about the evolution of galaxies and the origin of the enigmatic black holes located in their centres.

The EPTA is a collaboration of scientists from more than ten institutions across Europe and brings together astronomers and theoretical physicists to observe an array of pulsars 鈥� neutron stars in space that emit radio waves 鈥� with the specific goal of detecting gravitational waves.

The telescopes include, the Effelsberg Radio Telescope in Germany, the Lovell Telescope of the Jodrell Bank Observatory in the United Kingdom, the Nan莽ay Radio Telescope in France, the Sardinia Radio Telescope in Italy and the Westerbork Radio Synthesis Telescope in the Netherlands.

Combined, the pulsar observations construct a Galaxy-sized gravitational wave detector 鈥� spanning from the Earth to 25 carefully chosen pulsars across the Galaxy. This makes it possible to study gravitational waves with wavelengths much longer than those seen by other experiments.

Since the wavelengths are very long, the frequencies are very low, this is why it has taken many years to collect enough data for this new signal to become apparent.

The observations have been complemented by data from the Giant Metrewave Radio Telescope (GMRT) in India and provided by InPTA, leading to the development of a uniquely sensitive dataset. This announcement has also been coordinated with similar publications by other pulsar timing arrays across the world.

Although the analysis of the EPTA data presented today is in line with what astrophysicists expect, Prof Alberto Vecchio from the University of Birmingham, UK, nevertheless points out that 鈥渢he gold-standard in physics to claim the detection of a new phenomenon is that the result of the experiment has a probability of occurring by chance less than one time in a million.鈥� 

The result reported by EPTA - as well as by the other international collaborations - does not yet meet this criterion. To do so, the researchers aim to expand the current datasets in an International Pulsar Timing Array. This will exploit an array consisting of over 100 pulsars, observed with thirteen radio telescopes across the world, and agglomerating more than 10,000 observations for each pulsar, which should allow the astronomers to obtain irreproachable proof of having expanded the gravitational wave window on the Universe.