Dark energy: we may have detected it by chance, looking for something else

Dark energy: we may have detected it by chance, looking for something else
Dark energy: we may have detected it by chance, looking for something else

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

Photo: Hubble / ESA

Serendipity: accidentally bumping into something while looking for something else. The history of the science it is full of unexpected discoveries, governed not only by the competence and tenacity of the researchers, but also by a a bit of luck. And it could have happened again. A recent study, the result of experiments conducted in Gran Sasso workshops aimed at detect dark matter, has 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 the University of Cambridge, were published in Physical Review D.

Finding the dark matter under the Gran Sasso

The dark matter, that matter which is unable to emit radiation and which interacts only feebly with the 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 to indicate its existence, this one has not yet been proven. For this scientists seek particle interactions of dark matter with those of ordinary matter, using extremely sensitive detectors.

For this purpose, the Xenon scientific collaboration was born, involving 135 researchers from all over the world. The latest experiment conducted is Xenon1t: this is the largest particle detector built so far, consisting of a gigantic cylindrical metal container, which contains a detector composed of liquid xenon completely submerged in water, in order to obtain the clearest possible signals. Xenon1t has been active from 2016 to 2018 in the subsoil of National laboratories of the Gran Sasso of the National Institute of Nuclear Physics, in Abruzzo.

The detector was therefore primarily designed for find dark matter. However, in scientific research, the unexpected is often just around the corner. About a year ago, the experiment reported a 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 where this signal could be attributable to dark energyrather 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 is expanding at an accelerated rate. Usually, to research dark energy, scientists indagano the way 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 of 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, researchers say, could be dark energy.

The interpretation of strange results

Initially, in fact, to explain this phenomenon, scientists had resorted to assioni, hypothetical and extremely light particles produced in the Sun. However, experimental data from Xenon1t failed to justify the hypothesis of axions. Precisely for this reason the researchers constructed a physical model that the unexpected results of the experiment could have originated from dark energy particles produced in a region of Sole with strong magnetic fields.

It was really surprising that this excess could have been caused in principle by dark energy rather than dark matter – stated 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 fascinating, and not a demonstration. “We must first know that this was not simply a fluke – 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 demonstrate what is hypothesized from the model. If successful, it may be possible to directly detect dark energy within the next decade.

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