Researchers studying the sun may be one step closer to solving a decades-long mystery about the star: why its outer atmosphere, called the solar corona, is so much hotter than the layers below. "Thanks to this study, we may be one step closer to understanding the sun, the star that gives us life," said Professor Robertus Erdelyi from the University of Sheffield, co-investigator in the research.
The problem of coronal heating has been a puzzle for researchers for decades. The mystery is this: the diffuse cloud of charged atoms that make up the corona can reach temperatures of over 1,8 million degrees Fahrenheit (about 1 million degrees Celsius), while the sun's surface, called the photosphere, has a relatively moderate temperature of about 10.000 degrees Fahrenheit (or 6.000 degrees Celsius).
This contradicts stellar models, since the heat source of stars is nuclear fusion in their core; thus, temperatures should increase as we approach the center of a star. The layers of the sun seem to follow this rule until we reach the corona, which means there must be some unknown mechanism that heats the sun's outer atmosphere. And these snake-like magnetic phenomena could be the solution.
"A precise understanding of the magnetic field geometry is fundamental to understanding the various energetic phenomena that drive plasma dynamics in the solar atmosphere," said Erdelyi. "This includes the long-sought magnetic behavior that could ultimately be responsible for energizing the solar plasma at temperatures of millions of degrees."
Previous attempts to solve the coronal heating problem have focused on active regions of the sun, particularly sunspots, large dark patches on the face of the sun that are highly magnetic and transfer energy between the outer layers of the star. But for this new study, the research team turned their attention away from sunspots and focused on quieter regions of the sun.
These quiet areas of the photosphere are cover of convective cells called granules, which host weaker but more dynamic magnetic fields than those found around sunspots. Previous observations indicated that these magnetic fields are organized in small loops, but the study team discovered for the first time a more complicated underlying pattern, with the orientation of these magnetic fields displaying a serpentine variation.
"The more complex the small-scale variations in the direction of the magnetic field, the more plausible it is that energy is released through a process we call magnetic reconnection - when two magnetic fields oriented in opposite directions interact and release energy that contributes to atmospheric warming," said study co-investigator Michail Mathioudakis of Queen's University Belfast in Northern Ireland.
"We used the world's most powerful solar optical telescope to reveal the most complex magnetic field orientations ever seen at the smallest scales," added Mathioudakis. "This brings us closer to understanding one of the biggest puzzles in solar research."
