Has dark energy finally been detected? A new study suggests yes
Scientists have built a physical model to help explain the results, which may have originated from dark energy particles produced in a region of the Sun with strong magnetic fields, although they will be needed future experiments to confirm this explanation. Researchers say their study could be an important step toward detecting dark energy directly.
Everything our eyes can see in the skies and in our everyday world - from small moons to massive galaxies, from ants to blue whales - it makes up less than five percent of the universe. The rest is dark. About 27% is dark matter - the invisible force that holds galaxies and the cosmic web together - while 68% is dark energy, which causes the universe to expand at an accelerated rate.
" Although both components are invisible, we know much more about dark matter, since its existence was suggested as early as 1920, while dark energy was not discovered until 1998, ”said Dr. Sunny Vagnozzi of Kavli. Institute for Cosmology in Cambridge, the first author of the article. "Large-scale experiments like XENON1T have been designed to directly detect dark matter, looking for signs of dark matter 'hitting' ordinary matter, but dark energy is even more elusive."
To detect dark energy, scientists generally look for gravitational interactions. About a year ago, the XENON1T experiment reported an unexpected, or excess, signal against the expected background. “These kinds of excesses are often lucky breaks, but from time to time they can also lead to fundamental discoveries,” said Dr. Luca Visinelli, a researcher at the Frascati National Laboratories in Italy, 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.”
At the time, the most popular explanation for the 'excess were the axions - hypothetical extremely light particles - produced in the Sun. However, this explanation does not stand up to observations, since the amount of axions that would be needed to explain the XENON1T signal would drastically alter the evolution of stars much heavier than the Sun, in conflict with what we observe.
Photo credit - depositphotos .com We are far from fully understanding what dark energy is, but most physical models for dark energy would lead to the existence of a so-called fifth force. There are four fundamental forces in the universe, and anything that cannot be explained by one of these forces is sometimes referred to as the result of an unknown fifth force.
However, we know that the theory of gravity of Einstein works very well in the local universe. Therefore, any fifth force associated with dark energy is unwanted and must be "hidden" or "shielded" when it comes to small scales, and can only operate on the larger scales where Einstein's theory of gravity fails to explain the acceleration of the Universe. To hide the fifth force, many dark energy models are equipped with so-called screening mechanisms, which dynamically hide the fifth force.
Vagnozzi and his co-authors built a physical model, which used a type of screening mechanism known as chameleon screening, to show that dark energy particles produced in the Sun's strong magnetic fields could explain the excess of XENON1T. The researchers used their model to show what would happen in the detector if dark energy were produced in a particular region of the Sun, called the tachocline, where magnetic fields are particularly strong.
Their calculations suggest that experiments such as XENON1T, designed to detect dark matter, could also be used to detect dark energy. However, the original excess has yet to be convincingly confirmed. “First we need to know that this was not simply a fluke,” said Visinelli. "If XENON1T actually saw something, one would expect to see a similar excess again in future experiments, but this time with a much stronger signal."
If the excess was the result of dark energy , upcoming updates to the XENON1T experiment, as well as experiments pursuing similar goals such as LUX-Zeplin and PandaX-xT, should therefore be able to directly detect dark energy within the next decade.
