Barnard's Star - The Flare in 1998

The Flare in 1998

The observation of a stellar flare on Barnard's Star has added another element of interest to its study. Noted by William Cochran, University of Texas at Austin, based on changes in the spectral emissions on July 17, 1998 (during an unrelated search for planetary "wobbles"), it was four more years before the flare was fully analyzed. At that point Diane Paulson et al., now of Goddard Space Flight Center, suggested that the flare's temperature was 8000 K, more than twice the normal temperature of the star, although simply analyzing the spectra cannot precisely determine the flare's total output. Given the essentially random nature of flares, she noted "the star would be fantastic for amateurs to observe".

The flare was surprising because intense stellar activity is not expected around stars of such age. Flares are not completely understood, but are believed to be caused by strong magnetic fields which suppress plasma convection and lead to sudden outbursts: strong magnetic fields occur in rapidly rotating stars, while old stars tend to rotate slowly. An event of such magnitude around Barnard's Star is thus presumed to be a rarity. Research on the star's periodicity, or changes in stellar activity over a given timescale, also suggest it ought to be quiescent; 1998 research showed weak evidence for periodic variation in Barnard's Star's brightness, noting only one possible starspot over 130 days.

Stellar activity of this sort has created interest in using Barnard's Star as a proxy to understand similar stars. Photometric studies of its X-ray and UV emissions are hoped to shed light on the large population of old M dwarfs in the galaxy. Such research has astrobiological implications: given that the habitable zones of M dwarfs are close to the star, any planets would be strongly influenced by solar flares, winds, and plasma ejection events.