Providing a clue to why the Sun's corona is so much hotter than its surface, a study found that miniature solar flares called 'nanoflares' and the speedy electrons they produce may be the source of that heat.
A solar flare occurs when a patch of the Sun brightens dramatically at all wavelengths of light.
During these flares, solar plasma is heated to tens of millions of degrees in a matter of seconds or minutes.
Flares also can accelerate electrons (and protons) from the solar plasma at the speed of light.
Those speedy electrons also can be generated by scaled-down versions of flares called nanoflares.
"These nanoflares, as well as the energetic particles possibly associated with them, are difficult to study because we can't observe them directly," said Paola Testa from the Harvard-Smithsonian Center for Astrophysics (CfA) in the US.
Using the observations from the Interface Region Imaging Spectrograph (IRIS), the team found that IRIS provides a new way to observe the telltale signs of nanoflares by looking at the footpoints of coronal loops.
The team inferred the presence of high-energy electrons using IRIS high-resolution ultraviolet imaging and spectroscopic observations of those footpoint brightenings.
Using computer simulations, they also outlined the response of the plasma, confined in loops, to the energy transported by energetic electrons.
Finding high-energy electrons that aren't associated with large flares suggests that the solar corona is, at least partly, heated by nanoflares, noted the study.
The new observations help astronomers to understand how electrons are accelerated to such high speeds and energies - a process that plays a major role in a wide range of astrophysical phenomena from cosmic rays to supernova remnants, concluded the team.
The study appeared in the journal Science.
