Astronomers have reported the discovery of a new type of wave in the Sun. They have called them high-frequency retrograde (HFR) waves because they move in the opposite direction of the Sun’s rotation. And they appear as vortices – swirling patterns – on the surface of the Sun.
The waves have several unexpected characteristics, but the most puzzling is their speed. As reported in the journal Nature Astronomy, they move three times faster than Rossby–Haurwitz waves – stellar size waves that occur due to the Sun’s rotation on its axis. So how did they get so fast?
The team has put forward three possible explanations. The starting point is that these vortices are excited by the Coriolis force – the same force that on Earth makes fluid (such as air in a hurricane) swirl anticlockwise in the Northern hemisphere and clockwise in the Southern hemisphere.
This is not enough to speed up these waves so, the team put forward three potential modifiers for it. One thing could be magnetism. The Sun is after all a sphere of glowing plasma with strong magnetic fields that could play a role. The second one is another equally obvious explanation: gravity. The effect of the force could alter and enhance these vortices.
And finally, convection. Hotter plasma from the inner regions of the Sun rises and cooler plasma near the surface sinks, creating crucial motions within our star. This could influence the strength and speed of these waves. So what scenario do the observations prefer? None of these, apparently.
“If the HFR waves could be attributed to any of these three processes, then the finding would have answered some open questions we still have about the Sun,” lead author Chris Hanson, from New York University Abu Dhabi, said in a statement. “However, these new waves don’t appear to be a result of these processes, and that’s exciting because it leads to a whole new set of questions.”
The Sun has so many unanswered questions for us, and finding an answer is mostly just for the sake of knowledge. The Sun’s activity impacts life on Earth and given that it’s the closest star, the Sun is a window to all the other stars in the Universe.
“The very existence of HFR modes and their origin is a true mystery and may allude to exciting physics at play,” said Shravan Hanasoge, a co-author of the paper. “It has the potential to shed insight on the otherwise unobservable interior of the Sun.”