Sun's Coronal Loops Display Optical Illusion

The sun's corona is an extremely hot place, skyrocketing to temperatures in the millions of degrees. Now, scientists have taken a closer look at this star's outer atmosphere, examining the coronal loops that may contribute to these heated temperatures.

The sun's corona is unusual. While you'd think that the surface of the sun is hotter than its atmosphere, the opposite is actually the case. The surface is a relatively cool 10,000 degrees Fahrenheit. In contrast, the sun's atmosphere, also known as its corona, can be in the millions of degrees. The reason could be down to the coronal loops that can be seen in images of the sun.

Coronal loops are structures shaped like upside-down horseshoes that show where magnetic field lines are funneling solar gases or plasma. The best pictures of these loops suggest that they're a constant width--like strands of rope. Now, though, researchers have found that these loops may not be as uniform as we once thought. New research reveals that it's an optical illusion and, instead, the loops are actually tapered-wider at the top and narrower at the bottom.

"You need less energy to heat the corona if the loops have a tapered geometry, which is exactly what we found," said Henry Winter, the lead author of the study, in a news release.

In order to find out a little bit more about these loops and how effective they might be at heating the corona, the researchers constructed a computer model of a tapered loop using basic physics. They then processed their model to show how it would look when photographed by instruments. In the end, they found that even the best available images wouldn't have the resolution to show the loop's true structure, which explains why scientists have only recently discovered that the loops are tapered.

"Coronal loops are like Russian nesting dolls," said Winter. "We keep pulling them apart, but we haven't gotten to the smallest one yet."

The latest findings could explain exactly why the corona reaches such high temperatures. In addition, it reveals a little bit more about how the sun itself functions, which could be useful for better understanding space weather, such as solar flares and coronal mass ejections.

The findings were presented at a meeting of the American Astronomical Society Solar Physics Division in Montana.