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A team of researchers from New York University in Abu Dhabi, United Arab Emirates, has just made public the discovery of a strange type of solar waves high frequency never seen before. These are acoustic waves, they appear in the form of large vortices on the surface of the Sun, they move in the opposite direction to its rotation and, most enigmatic, they move three times faster than current theories predict.
In a study recently published in ‘Nature Astronomy’, scientists explore the three possible mechanisms that would explain these waves, but none of them fit the observed data. The available theories are simply not capable of determining the origin of
these ‘whirlpools’, which remain a mystery. The finding suggests the existence of a whole new solar physics yet to be discovered.
Together with his colleagues, Chris Hanson, first author of the study, refers to the phenomenon as ‘high frequency retrograde vorticity waves’. Analysis of data from several decades of solar observations showed that other similar waves move around the Sun three times as slowly, so the phenomenon cannot be explained by current models of plasma motion.
The difficult observation of the Sun
Since it is not possible to observe the interior of the Sun, its internal mechanics is inferred from the activity that takes place on the surface. And the acoustic waves contain valuable information about what may be happening ‘down there’. They are usually generated near the surface and are then reflected inward, where they resonate, creating acoustic oscillations that can reveal features of the Sun’s interior.
That is precisely what the scientists were doing by analyzing ten years of data from the Helioseismic and Magnetic Imager satellite. But in them they found a very consistent signal that revealed the presence of a type of wave never seen before.
The researchers tested three possible explanations: that the waves were caused by magnetic fields inside the Sun; that come from other solar waves called gravity waves; or that are due to compression of the plasma. But none of these ideas match the data.
“Finding a set of waves that has no explanation,” says Hanson, “is…exciting and intriguing, because now the challenge remains to explain what they are. We were missing an ingredient in our understanding of the Sun.”
The solution, on Earth?
Interestingly, the solution to the mystery could be found right here on Earth. In fact, a similar type of wave, called Rossby wave, appears to exist in our planet’s oceans, which also travel much faster than researchers can explain. “In the absence of a solution for both these fast-moving solar waves and the Rossby ocean waves says Hanson, “we can only say that the similarities are worth investigating.”
However, the scientist believes that it is still possible that the solution to the enigma goes through some kind of combination between magnetism, gravity and compressionalthough you can’t be sure. “It’s very hard to imagine a scenario where one of these factors doesn’t play some sort of role in turning on this ‘speed mode’,” he explains. But the researchers couldn’t think of any other plausible mechanisms, so they hope that new and more detailed analyzes can explain these strange waves in the future.
Shravan Hanasoge, co-author of the research, states for his part that “the very existence of high-frequency retrograde waves and their origin is a true mystery and may indicate that there is an exciting new physics at play. One with the potential to shed information about the otherwise inaccessible interior of the Sun”.
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