What Flares May Tell

"This is a flare," says Mercedes Richards. She holds up a photograph of a glowing sphere—a star with a flaming, orange arch leaping out from its surface. "It's an enormous event on a star," says Richards, professor of astronomy and astro-physics at Penn State. "Normally gas flows in a loop like this one, but sometimes the energy is released. Imagine a pair of scissors snipping the top of the arc. When the scissors snip, the gas flows right out into space."

giant red ball of fire

A solar flare: superheated gas erupts in a fiery loop from the surface of a star.

Cool stars like our Sun have powerful magnetic fields that cause solar flares to occur, Richards explains. These fields produce currents that cycle hot gases much like boiling water in a stove-top pot. As water heated at the bottom of the pot rushes to the top, so gases superheated at a star's core rise to its surface. The chromosphere and the corona, a star's outer-most layers, produce flares that burst out with tremendous force. Charged particles from the explosions carry great distances through space before cooling.

"When a flare passes by the Earth, these particles are funneled toward the poles by Earth's magnetic field," Richards says. Earth-bound observers are treated to beautiful displays of aurorae—radiant lights in the night skies of both hemispheres.

But the charged particles also interrupt satellite signals, causing momentary lapses in television reception and military communications. "That's why solar physics is funded by the defense industry," Richards says. "The military wants to know when these interruptions are going to occur."

To learn more about when and how flares occur, Richards surveyed binary stars using a pair of telescopes at the National Radio Astronomy Observatory in Green Bank, West Virginia. Binaries are systems composed of two stars bound together by gravity. The pull between them causes the smaller star of the pair to lose hydrogen to its larger companion as they spin around one another.

Accelerated growth causes the larger star to age and ultimately to die faster. "We can see the entire lifespan in a relatively short amount of time," Richards says. "I would've needed to observe the Sun for 100 years to obtain the information I got from studying binary stars for five years."

Solar physicists have found a correlation between the occurrence of flares and sunspots, another phenomenon associated with the sun's magnetic field. "Sunspots are footprints of magnetic fields that emerge on the surface of the Sun," she observes. They appear frequently at low latitudes, decreasing in strength and number as they move toward the Sun's equator. Every 11 years, the sunspots completely disappear at the equator and the process begins again.

Flare activity is usually at its peak when the number of sun-spots is also at its peak; flares are less frequent when the sun-spots disappear. The cycle, she says, is the same for the two phenomena. Richards' study of flares on distant stars will allow scientists to predict when flares will occur. This information can be used to surmise how often flares occurred on the Sun in the distant past. And tracking flares on the sun at various points in its 4.6 billion year history, she says, will improve our understanding of Earth's evolution.

When the Earth was young and had no atmosphere, solar flares would have significantly impacted the planet's surface temperature, she explains, and therefore, life on Earth: "By including these new results about flares on distant stars, we'll be able to produce more accurate models of the environment in which life developed on Earth. We might also be able to predict the conditions under which life could evolve in other planetary systems around other stars."

Mercedes Richards, Ph.D., is professor of astronomy and astrophysics in the Eberly College of Science, 525 Davey Lab, University Park, PA 16802; 814-865-0150; mtr11@psu.edu.

Last Updated May 01, 2004