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According to our best understanding of the universe, five-sixths of all matter out there is dark matter. This is an invisible substance that we are yet to confirm exists. The only force it interacts with is gravity and new research proposes that this gravitational interaction might not be exactly conventional.
As reported in The Astrophysical Journal, researchers from Italy propose the so-called non-minimal coupling between gravity and dark matter. This means dark matter's gravitational influence and how it affects space-time is different from the minimal coupling between gravity and regular matter that makes us and the rest of the universe.
Astronomers’ observations of the way galaxies rotate suggest that there should be a lot more matter out there than we can actually see with our telescopes. Work done by Vera Rubin, Kent Ford, and Ken Freeman in the 1960s and 1970s has not only been confirmed but even more evidence has since suggested that dark matter ought to be out there.
Despite being hypothesized five decades ago, we are yet to find exactly what dark matter is. And there have been suggestions that maybe we don’t need dark matter at all to explain what we observe in the universe. We need to change our formulations of the laws of gravity. Gravity is at the center of this and it might be the key to understanding what is going on.
“For this reason,” authors Giovanni Gandolfi, Andrea Lapi, and Stefano Liberati said in a statement, “we asked ourselves: is gravity wrong or are we just missing something crucial about dark matter's nature? What if dark matter and standard 'baryonic' matter do not communicate in the way we have always imagined?. With our research, we have tried to answer these intriguing questions”.
Their model seems to be broadly consistent with the observations and can explain the properties of different types of galaxies, which is an important first test for a new approach to dark matter. And while non-minimal coupling has not been a conventional description for dark matter, such an idea has been floated before for other unexplained stuff in the universe.
“This feature of dark matter is not a piece of new exotic fundamental physics,” the authors said. “One can explain the existence of this nonminimal coupling with known physics alone”.
The true test of a hypothesis, once it can explain what we see, is the power of predicting what we are yet to discover. But the team is certainly confident that this model will continue to bear fruit.
“The future of dark matter looks brighter” the authors concluded. “Further studies will be carried out to explore all the interesting implications of this proposed new feature of dark matter. We wouldn't be surprised to discover that this non-minimal coupling could solve other unanswered questions of the Universe”.
