Tiny red dwarf stars can still unleash powerful stellar flares

Red dwarf stars, despite their small size and relatively lesser power, can unleash enormous amounts of energy that approach the equivalent of 100 million atomic bombs, according to a news release from the Space Telescope Science Institute (STScI).

Astronomers from the University of Washington and STScI have made new observations on the activity of red dwarfs. Using data collected by the Hubble Telescope in 2006 for the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS), the collaboration found a number of important characteristics regarding the volatility of red dwarfs in comparison to their younger and brighter counterparts, such as our own sun.

SWEEPS data was originally collected for an extra-solar planet survey, yet yielded information useful for studying flares from red dwarf planets, a project differing from previous studies that focused on younger, brighter stars.

Collected over a period of seven days, the SWEEPS data provided the astronomers with information about the light emanating from 215,000 red dwarfs. Slight increases in the brightness of the stars observed indicated flares, with around 100 counted by the astronomers.

Stellar flares occur when interactions in a star’s magnetic field cause bursts of plasma to eject from the surface of a star to a significant distance around it. Significant amounts of radiation can emanate from the bursts, including X-rays, gamma rays and charged particles known as solar wind.

Flares can have a significant impact on the solar weather for planets that orbit a particular star, strongly changing conditions for the duration of the burst. Solar flares, which are specific to our sun, can disrupt certain radio communications, affect satellite movements and endanger astronauts in the middle of space walks.

Red dwarfs flare about 15 times less often than younger stars, with a flare resulting in a ten percent increase in brightness; this increase is proportionally much greater than flares from the sun.

Certain stars that oscillated in their brightness, termed variable stars, tended to flare much more often by about a thousand-fold than other red dwarfs. Magnetic fields of stars, the major driving force of flares, are much stronger in red dwarfs than in younger stars.

Convection zones, where hot gas bubbles make their way from the insides of a star to the surface, are much deeper in red dwarfs proportionally than other stars, producing starspots that can cover up to half of the star and lead to flaring. For comparison, sunspots cover only less than one percent of the sun’s surface.

Stellar flares from red dwarfs, with their great intensity, can have a much more significant impact on orbiting planets than solar flares do on ours.

Energy from a stellar flare can cause the atmosphere of a nearby planet to expand and be forced away from the planet.

While flares may not be as common among the very old red dwarfs as they are among younger stars, they are still able to unload a lot of heat.