LASP researcher reveals new clues on what makes the Sun’s atmosphere so hot

This story was adapted from one published by Rice University. Read the original version here.

New research appears today in the Journal Nature Astronomy that may help resolve a long-standing mystery about the Sun: Why the solar atmosphere is millions of degrees hotter than the surface.

The study was led by Shah Bahauddin, a former graduate student at Rice University, and now a solar researcher at the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado, Boulder.

Image of the active Sun (Credit NASA)

“The heating of solar atmosphere remains one of the most daunting problems in modern astrophysics,” said Bahauddin 

In the new study funded by NASA, Bahauddin and his colleagues Stephen Bradshaw at Rice University and Amy Winebarger at NASA’s Marshall Space Flight Center studied images from the Earth-orbiting imagers Interface Region Imaging Spectrograph (IRIS) and the Atmospheric Imaging Assembly (AIA) that show evidence of a super-heated solar atmosphere in relation to the Sun’s surface.  

The images show that heavier ions in the solar atmosphere transition region (between the Sun’s chromosphere and corona) are preferentially heated in low-lying magnetic loops that produced pockets of super-hot plasma up to millions of degrees Kelvin. 

For the first time details of these transition region loops were resolved and the researchers were able to analyze the movements and temperatures of ions within the loops via the light they emit, read as spectral lines that serve as chemical “fingerprints.”

A video of the phenomenon (also depicted in the image) illustrates the details of how low-lying loops of plasma are energized.

Images of the sun captured by the IRIS mission show new details of how low-lying loops of plasma are energized and may also reveal how the hot corona is created. (Credit: Rice University/NASA)

“It’s in the emission lines where all the physics is imprinted,” said Bradshaw, an associate professor of physics and astronomy at Rice University. “The idea was to learn how these tiny structures are heated and hope to say something about how the corona itself is heated. This might be a ubiquitous mechanism that operates throughout the solar atmosphere.”

The researchers describe “brightenings” in the reconnecting loops that contain strong spectral signatures of oxygen and, especially, heavier silicon ions. There, loops of magnetized plasma arc continuously, not unlike their cousins in the corona above. They’re much smaller and hard to analyze, but have long been thought to harbor the magnetically driven mechanism that releases bursts of energy in the form of nanoflares.

“This discovery enabled us to draw a clear picture of how tiny, low-lying, cool structures in the Sun can produce super-hot plasma and supply an immense amount of energy and momentum to the upper solar atmosphere” Said Bahauddin, a research scientist at LASP. “As our society becomes more dependent upon satellites and space instruments, we increasingly need to understand how the sun affects our space weather as well as predict its future activities.”