Solar flares are large storms on the sun that can affect us here on Earth, interfering with cell phone service, radio and GPS navigation systems. Unlike other space weather events, radiation from solar flares travels at the speed of light. We get no warning that they’re coming.
In a study published in the Astrophysical Journal Letters in April, New Mexico State University astronomers’ research about an electromagnetic phenomenon called a “current sheet,” provides support for the computer models that may eventually be used to predict solar flares before our communications can be disrupted.
“The existence of a current sheet is crucial in all our models of solar flares so these observations make us much more comfortable that our models are good,” said James McAteer, NMSU assistant professor of astronomy in the College of Arts and Sciences, author of the study with lead author NMSU post doctoral researcher Chunming Zhu.
A NASA news release describes the current sheet as a very fast, very flat flow of electrically-charged material, defined in part by its extreme thinness compared to its length and width. Current sheets form when two oppositely-aligned magnetic fields come in close contact, creating very high magnetic pressure. Electric current flowing through this high-pressure area is squeezed, compressing it down to a very fast and thin sheet. It’s a bit like putting your thumb over the opening of a water hose – the water, or, in this case, the electrical current, is forced out of a tiny opening much, much faster. This configuration of magnetic fields is unstable, meaning that the same conditions that create current sheets are also ripe for magnetic reconnection.
“Magnetic reconnection happens at the interface of oppositely-aligned magnetic fields,” said Zhu. “The magnetic fields break and reconnect, leading to a transformation of the magnetic energy into heat and light, producing a solar flare.”
In December 2013, three NASA solar observatories captured the most comprehensive observations of the phenomenon known as a current sheet, strengthening the evidence that scientists’ understanding of solar flares is correct. Those three solar-watching missions are NASA’s Solar Dynamics Observatory, or SDO, NASA’s Solar and Terrestrial Relations Observatory, or STEREO – which has a unique viewing angle on the far side of the sun – and JAXA/NASA’s Hinode.
This isn’t the first time scientists have observed a current sheet during a solar flare, but this study is unique in that several measurements of the current sheet – such as speed, temperature, density, and size – were observed from more than one angle or derived from more than method.
“You have to be watching at the right time, at the right angle, with the right instruments to see a current sheet,” said McAteer. “It’s hard to get all those ducks in a row.’
Zhu is among a number of researchers McAteer has recruited to the university through his $750,000 National Science Foundation CAREER award. The award supports faculty who integrate research creativity and innovative teaching and allows professors to support graduate students and hire postdoctoral researchers.
Zhu discovered NMSU in 2011 when the university hosted an international Solar Physics Division meeting. The beauty of the campus and McAteer’s reputation with Zhu’s doctoral adviser and another professor at Rice University encouraged Zhu to pursue his research at NMSU.
“It has been my great pleasure to work with Dr. McAteer,” Zhu said. “His expertise and encouragement have been very helpful for me to continue the research.”
Thanks to the NSF award, McAteer has gathered researchers at NMSU to look at two problems: the dichotomy between the outer parts of the sun that are hotter than the core and the question of how solar storms are powered.
The latest investigations of the current sheet phenomenon provide supportive evidence as McAteer and his team continue to analyze solar observations and test equations, which may lead to new ways of predicting solar storms in the future.
