BOULDER, Colo. (KDVR) – A team of some 1,000 undergraduate students at the University of Colorado Boulder were recruited by a team of physicists to help solve a mystery about the sun.

The question has long puzzled even veteran astrophysicists: How can the surface of the sun be cooler than its outermost atmosphere?

Students at CU Boulder contributed an estimated 56,000 hours researching, and what they found challenged a popular astrophysics theory.

The contradicting theory

Telescopic evidence suggests the outermost atmosphere, or corona, burns at temperatures in the millions of degrees Fahrenheit. Yet, the surface of the sun is much cooler at only thousands of degrees, according to CU Boulder.

“That’s like standing right in front of a campfire, and as you back away, it gets a lot hotter,” said James Mason, the lead author of the study and an astrophysicist at the Johns Hopkins University Applied Physics Laboratory.

The popular theory suggests that tiny flares that are too small for telescopes to spot may be responsible, with enough consistency they could make the corona hot. But Mason said the students’ results made him doubt this theory.

“The evidence from our paper suggests the opposite. I’m a scientist. I have to go where the evidence is pointing,” Mason said.

How they did it

From 2020 to 2022, students studied over 600 solar flares and the results suggested that solar flares may not be responsible for superheating the sun’s corona.

They worked in small teams to compute the energy of single flares and peer-reviewed their findings. Then each case was reviewed by the senior authors who compiled the results to be analyzed and presented.

With those findings, they added up how much heat each of those flares could contribute to the sun’s corona.

What they found

The study, published May 9 in The Astrophysical Journal, suggests that solar flares may not be responsible for superheating the sun’s corona. Instead, Alfvén waves were found as the dominant mechanism for coronal heating.

“We found a preflare-subtracted, flare energy frequency distribution with a slope of 1.63 ± 0.03, which suggests Alfvén waves play an important role in heating the solar corona,” the study reads.

In short, their calculations showed that the sum of the sun’s nanoflares likely wouldn’t be powerful enough to heat up its corona to millions of degrees Fahrenheit.

The study notes that their results contradict popular theories, despite widespread knowledge that the underlying physical processes should be the same for the sun as other stars.

“We argue that this discrepancy is likely due to differences in methodology and observational availability,” the study read.

More information about this study and the methodology can be found on the CU Boulder website or in its official publication in The Astrophysical Journal.