Where do high-energy particles that endanger satellites, astronauts and airplanes come from?
For decades, scientists have been trying to solve a vexing problem about the weather in outer space. At unpredictable times, high-energy solar particles bombard Earth and objects outside Earth’s atmosphere with radiation that can endanger the lives of astronauts and destroy satellites’ electronic equipment.
These flare-ups can trigger showers of radiation strong enough to reach passengers in airplanes flying over the North Pole. Despite scientists’ best efforts, a clear pattern of how and when these flare-ups will occur has remained difficult to identify.
Now, in U.S. National Science Foundation-supported research reported in The Astrophysical Journal Letters, authors Luca Comisso and Lorenzo Sironi of Columbia University document when and how high-energy particles are born in turbulent environments like that of the sun. The findings pave the way for more accurate predictions of when dangerous bursts of these particles will occur.
"This research will allow us to better predict the origin of solar energetic particles and improve forecasting models of space weather events," Comisso said.
Comisso and Sironi demonstrated that magnetic fields in the outer atmosphere of the sun can accelerate ions and electrons up to velocities close to the speed of light. The sun and other stars’ outer atmospheres consist of electrically charged particles in a plasma state, a turbulent state distinct from liquid, gas and solid states.
Scientists have long believed that the sun’s plasma generates high-energy particles. But particles in plasma move so erratically and unpredictably that until now they have not been able to demonstrate how and when this occurs.
Comisso and Sironi created computer simulations that show the exact movements of electrons and ions in the sun’s plasma. The simulations mimic the atmospheric conditions on the sun and provide the most extensive data gathered to date on how and when particles are accelerated to very high energies.
"Cosmic acceleration of high-energy particles is a mystery that has puzzled scientists for more than a century," said Vyacheslav Lukin, an NSF program director for Plasma Physics. Although the research focuses on the sun, further simulations could be run in other contexts, the scientists said, to understand how and when distant stars, black holes and other entities in the universe generate bursts of energy.