Consider the following: A hot cup of coffee burns your tongue a bit, so you put it down. Then you notice that the steam rising from the mug is somehow hotter than the coffee itself — so much hotter, in fact, that it sears everything within reach of the blistering steam.
For well over half a century, one of the most baffling riddles in science has been hanging over our heads. The Sun’s corona — the hazy atmospheric layer extending hundreds of thousands of kilometers from the Sun’s surface — is 1,000,000°C. The actual surface of the Sun, from which the corona emanates, however, is a relatively cool 6,000°C. This occurrence defies common sense (and the second law of thermodynamics), because heat is not supposed to flow from something that is hot to something that is hotter.
Coronal loops made of blisteringly hot, electrically charged gas. Credit: Trace Team/NASA
But a team of researchers from Queens University Belfast might have unraveled this enigma. Using the Swedish Solar Telescope in the Canary Islands, the group detected the presence of abnormally strong magnetic oscillations originating at bright points on the Sun’s photosphere, or visible surface. These oscillations were characterized as Alfvén waves — a type of purely magnetic wave that is rife with energy. If bright points are present in abundance, they can simultaneously propel Alfvén waves, in a geyser-like fashion, into the corona, sustaining its scorching temperature.
Solar physicist David Jess, who led the study, calls it the first “unambiguous and concrete detection” of Alfvén waves in the Sun’s atmosphere.
Alfvén waves have long featured prominently in the quest to solve the coronal heating problem. The waves are incompressible — a characteristic that allows them to propagate the necessary distances to heat the corona. This property also makes them difficult to detect.
“The real excitement is that even though this theory was predicted in the early 1940s, it’s really just within the last couple of years that these new facilities on Earth have provided the evidence,” says Jess.
The more we understand our Sun, the better we can mimic its modus operandi. Alfvén waves exist whenever a magnetic field is strong enough to support them. Since the Earth has a magnetic field of its own, we have a steady supply of Alfvén waves as well.
“If these reactions can be contained here on Earth, then perhaps this will open the gateway to being able to naturally sustain nuclear reactions on Earth,” Jess says. That way, he says, the nuclear reactions can be generated again and again.
The challenge with current nuclear fusion reactors is to sustain the energy created and keep it in places where it can be converted into heat and energy, then distributed to people’s homes. But because Alfvén waves are magnetic in nature, Jess says, they can be trapped with magnetic or electric fields, preventing energy from being wasted outside the reactions. A better understanding of how these mysterious waves work may one day lead to a perpetual supply of naturally sustained nuclear energy.
Alfvén Waves in the Lower Solar Atmosphere
Science March 20, 2009
Originally published April 1, 2009