We may have detected dark energy by chance, looking for something else

We may have detected dark energy by chance

A team of researchers from Cambridge University has obtained an unexpected result from experiments conducted under the Gran Sasso to find dark matter: dark energy could be responsible

Photo: Hubble / ESA Serendipity: running into fortuitously into something, while looking for something else. The history of science is full of unexpected discoveries, governed not only by the competence and tenacity of the researchers, but also by a bit of luck. And it could have happened again. A recent study, the result of experiments conducted in the Gran Sasso laboratories aimed at detecting dark matter, reported unexpected data. The culprit could be dark energy, the mysterious force that accelerates the universe and escapes the investigation of cosmologists and astrophysicists. The results of the study, conducted by a team of researchers from Cambridge University, were published in Physical Review D.

Finding dark matter under the Gran Sasso

Dark matter, that matter which is unable to emit radiation and which interacts only feebly with gravitational force, is considered one of the main constituents of the universe, five times more abundant than ordinary matter. Although there are numerous astrophysical observations indicating its existence, this has not yet been proven. For this scientists are looking for interactions of dark matter particles with those of ordinary matter, using extremely sensitive detectors.

The scientific collaboration Xenon was born for this purpose, involving 135 researchers from all over the world. The last experiment conducted is Xenon1t: it is the largest particle detector built to date, consisting of a gigantic cylindrical metal container, which contains a detector made up of liquid xenon completely submerged in water, in order to obtain the clearest possible signals. Xenon1t was active from 2016 to 2018 in the subsoil of the Gran Sasso National Laboratories of the National Institute of Nuclear Physics, in Abruzzo.

The detector, therefore, was mainly designed to find dark matter. However, in scientific research, the unexpected is often just around the corner. About a year ago, the experiment reported an unexpected signal, also called excess, compared to what was expected. “These types of excesses are often fortuitous, but from time to time they can also lead to fundamental discoveries - said Luca Visinelli, co-author of the study -. We explored a model in which this signal could be attributable to dark energy, rather than the dark matter that the experiment was originally designed to detect ".

The elusive dark energy

There is not only dark matter: it is estimated, in fact, that 68% of the universe is made up of dark energy, which causes the universe to expand at an accelerated rate. Usually, to search for dark energy, scientists investigate how gravity attracts objects. On very large scales, in fact, the gravitational effect of dark energy would be repulsive, accelerating the expansion of the universe.

However, this energy is even more elusive than dark matter. "Although both components are invisible, we know much more about dark matter, as its existence was suggested as early as the 1920s, while dark energy was not discovered until 1998," said Sunny Vagnozzi, first author. of the article. Yet one way to justify the excess found in Xenon1t, according to the researchers, could be precisely dark energy.

The interpretation of the strange results

Initially, in fact, to To explain this phenomenon, scientists had resorted to axions, hypothetical and extremely light particles produced in the Sun. However, experimental data from Xenon1t could not justify the hypothesis of axions. Precisely for this reason, the researchers constructed a physical model according to which the unexpected results of the experiment could have originated from dark energy particles produced in a region of the Sun with strong magnetic fields.

“It was really surprising that this excess may have been caused in principle by dark energy rather than dark matter - said Vagnozzi -. When things fit together like this, it's really special. “However, one cannot sing victory. For the moment it is an interpretation of results, albeit a fascinating one, and not a demonstration. “We must first know that this was not simply a stroke of luck - continues Visinelli -. If Xenon1t really detects something, you would expect to see a similar excess again in future experiments, but this time with a much stronger signal. ”The next step, therefore, is to demonstrate what the model assumes. If successful, it may be possible to directly detect dark energy within the next decade.




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