Shedding light on solar flares

Astrophysicists at the University of Glasgow are investigating auroras to better understand the mechanism behind energy transport in solar flares.

Researchers from the University’s School of Physics and Astronomy suggest, in a paper published in the Astrophysical Journal, that magnetic waves, which cause auroras to form on Earth, could help energy from solar flares travel tens of thousands of kilometres in under a second.

Although solar flares are rare, they can cause immense damage to power grids and satellites.

“What astrophysicists want to know is how does flare energy get from high above the Sun’s visible surface, where it is released, down to just above the surface, where it is then radiated into space?” said Alexander Russell, Royal Commission for the Exhibition of 1851 Research Fellow at the University.

Solar flares are the biggest explosions in the solar system, filling it with UV light, X-rays and high-energy particles.

The current theory is that the flare accelerates electrons to high speeds and the electrons then carry the energy with them. However, if this was the case, beams of electrons would likely disrupt themselves if carrying the full flare energy. The researchers are trying to ascertain another way that at least some of the energy can travel.

During auroras, commonly known as the Northern or Southern lights, magnetic waves carry energy downwards along the Earth’s magnetic field. When this is released at fairly low altitudes of between 100 and 10,000 km, it produces the aurora’s vibrant colours.

Understanding the auroras on Earth has allowed the researchers to build computer models of the solar atmosphere. When they simulate magnetic waves within this model, the waves carry energy towards the Sun’s surface heating up a low-temperature layer called the chromosphere. When the temperature of this layer increases, it gets brighter and brighter, contributing to the flare.

“The heating we find is particularly targeted at that part of the atmosphere that produces visible ‘white-light’ emission. This is an important finding because this region is known to heat during flares, but cannot be reached by electrons,” explained Lynday Fletcher, also at the University, who originally conceived the idea that magnetic waves transport energy in solar flares.

Reference: Propagation of Alfvénic Waves from Corona to Chromosphere and Consequences for Solar Flares