Our Sun may be wider at the middle than at its poles than previously thought, raising new questions about activity inside the star, a new study using data from NASA's Solar Dynamics observatory showed.

Researchers said the data measured the sun's shape from 2010 to 2012, during which sunspot activity evolved from a minimum to a maximum.

"The peculiar fact that the sun is slightly too round to agree with our understanding of its rotation is also an important clue in a longstanding mystery. The fact that it is too round means that there are other forces at work making this round shape," study lead author Jeffrey Kuhn told Space.com.

"We've probably misunderstood how the gas turbulence in the sun works, or how the sun organizes the magnetism that we can only see at the surface. Finding problems in our theories is always more exciting than not, since this is the only way we learn more," added Kuhn, a physicist and solar researcher at the University of Hawaii in Pukalani.

The researchers detailed their research online in the Aug. 16 edition of the journal Science.

Until now, astronomers had presumed the shape of the sun changed along with 11-year-long solar cycles where the number of sunspots can rise and fall dramatically.

Yet, for more than 50 years, researchers have found it difficult to measure the sun's shape.

"So far, just about anything we measure with sufficient accuracy about the sun ends up varying with the 11-year sunspot rhythm," Kuhn said.

"There are literally tens of measurements, and most of them don't agree. Most of the differences are attributable to how hard it is to see small shape changes through the atmosphere," he added.

'Flattened' sun

Kuhn and his colleagues also found the Sun's slightly flattened shape — with a wide equator and a shorter distance between its poles — is remarkably stable and nearly completely unaffected by the solar cycle.

This suggests the shape of the sun "really is controlled by fundamental properties of the star, and not so much by the sun's perhaps superficial magnetism, which is highly variable," Kuhn said.

Yet, the Sun's shape is still rounder than theory had predicted, the researchers said.

Future research to measure the sun's shape more accurately can also help analyze how oscillations from deep in the sun's interior are manifested at its surface.

"This will be a new and powerful tool for understanding why the sun changes, and how it will affect the Earth in the future," Kuhn said. - BM, GMA News