Without the Sun, life on Earth would be impossible. But few of us understand what happens on its surface.
New research has uncovered high-frequency waves that curl around the Sun and could even stretch deep into its heart, and they appeared to travel much faster than predicted by theory.
Teams from New York University Abu Dhabi are behind the discovery, which was detected after a team of researchers looked through a quarter of a century’s data.
Appearing as either anti-clockwise or clockwise motion, they exist both above and below the Sun’s equator, the scientists revealed in a newly published paper with the findings surprising even them.
“We weren’t looking for them originally,” said Dr Chris Hanson, a research associate in NYUAD’s Centre for Space Science and the study’s first author. “It’s something beyond what we were expecting.”
The waves are termed “retrograde” because they move across the surface in the opposite direction to the sun’s rotation.
The researchers looked at data from telescopes across the globe that continuously record data on the Sun. Small shifts in the sound waves on the Sun’s surface allowed the researchers to detect the high-frequency retrograde (HFR) waves.
Dr Hanson said it is comparable to the way that geophysicists detect oil underground. Large vibrations are generated on the surface of the Earth and these travel down and back up again, and if they pass through oil, the sound wave changes slightly.
Clues about behaviour of the Sun
The HFR waves are found in the same way and may be present through the whole of the Sun’s convective zone, which covers its outer 30 per cent. There are two other main sections, the middle radiative zone and the inner core.
However, the data used in the study covers just the outer three per cent of the sun, so it remains unclear how deep they exist. But detecting them on the surface may still offer clues about the internal behaviour of the Sun.
“In theory, they could be going very deep,” said Dr Hanson. “Unfortunately they’re very weak so we’ve not been able to look that much deeper.”
Astrophysicists already knew of different types of wave on the Sun’s surface, called Rossby waves, which are larger than the HFR waves and travel across the surface in the opposite direction to the sun’s rotation.
How the Sun behaves is of more than academic significance, because disturbances on its surface, such as those that cause solar storms — events when the sun gives off large amounts of electromagnetic radiation — affect Earth, such as by creating electrical surges.
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Like the Sun, the Earth has waves on its surface consisting of movement of air and water that generate currents and wind patterns.
However, whether other stars exhibit similar patterns of movement to the Sun is unclear. Finding out is extremely difficult because the distances involved are so huge.
The second-closest star, Proxima Centauri, at a distance of more than 4.2 light years, is more than 260,000 times further from Earth than the Sun.
“The other stars, they’re very, very far away,” said Dr Hanson. “We don’t get that spatial resolution. It would be great if we could see these waves in other stars.
“There are oceanic and atmospheric waves. These patterns in other astrophysical bodies, it’s certainly possible.”
The challenge now is to understand how the HFR waves are formed. Researchers will produce mathematical models to simulate wave motion in the Sun and the hope is that as additional elements are added to the calculations, the waves will “pop up”, indicating which astrophysical phenomenon causes them.
“In our minds, we don’t know what ingredients cause it,” said Dr Hanson. “We’ll add all kinds of ingredients and see what causes it.”
For Dr Hanson, who has been studying the Sun for more than a decade, our nearest star remains “quite a unique laboratory”.
“The physics found on the Sun are very hard to replicate on Earth,” he said. “It’s an astrophysical body we can learn so much from.”
Dr Hanson and the study’s other authors, Dr Shravan Hanasoge, co-principal investigator of the Centre for Space Science, and Prof Katepalli Sreenivasan, the centre’s principal investigator, have published their findings in Nature Astronomy.
They carried out their work in collaboration with the Tata Institute of Fundamental Research in India, with which Dr Hanasoge is associated.