European Space Agency: Giant solar eruption seen by Solar Orbiter
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The interior of the Sun — as with other stars — is not something that can be imaged by conventional astronomical methods like optical or X-ray telescopes. Accordingly, scientists rely on studies of the surface signature of various waves moving within the Sun to learn more about what happens inside the star, much like how geologists use seismic waves to infer the structure of the Earth’s interior. In this way, analysing the newly identified waves in the Sun could help improve our understanding of the nature and evolution of stars.
The study was undertaken by solar physicist Dr Chris Hanson of the New York University (NYU) Abu Dhabi’s Center for Space Science, and his colleagues.
To identify the waves, the team analysed 26 years’ worth of data collected by both ground and space-based telescopes.
The motions — dubbed high-frequency-retrograde vorticity waves — manifest themselves as a pattern of swirling vortices on the surface of the Sun, near the star’s equator, each of which forms a little cell.
Each wave, the researchers said, moves the opposite direction to the Sun’s rotation, meaning that the motions in the star’s northern hemisphere are anti-symmetric to those seen in the southern hemisphere, and penetrate to a depth of three percent of the solar radius.
But their most curious feature is that they move three times faster than can be explained by hydrodynamic theory alone.
According to the team, complex interactions between other, better-known solar waves and either convection, magnetic fields or gravitational forces could potentially drive the high-frequency-retrograde waves at this speed.
Dr Hanson said: “If the high-frequency-retrograde 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.”
He added: “However, these new waves don’t appear to be a result of these processes.
“That’s exciting because it leads to a whole new set of questions.”
Astrophysicist Dr Shravan Hanasoge, also of NYU Abu Dhabi, is a co-author of the research paper.
He said: “The very existence of high-frequency-retrograde modes and their origin is a true mystery.”
Their presence, he added, “may allude to exciting physics at play.
“It has the potential to shed insight on the otherwise unobservable interior of the Sun.”
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The researchers added: “There are evidently missing, or poorly constrained, ingredients in the standard models of the Sun and determining the mechanism responsible for high-frequency-retrograde modes will deepen our understanding of the interiors of the Sun and stars.
“Interestingly, the Sun is not unique in exhibiting such high-frequency modes of undetermined origin. For instance, the discovery of unexplained high-frequency Rossby-like waves in the ocean continues to puzzle atmospheric scientists three decades on.
“Oceanic Rossby waves above tropical latitudes exhibit high phase speeds, up to four times greater than that of the standard Rossby theory.
“Drawing from the atmospheric literature may thus help us better understand the physics driving high-frequency-retrograde waves.”
The full findings of the study were published in the journal Nature Astronomy.
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