June 14, 2013
Nearby Flare Star Gives Off Explosive Burst Of Light
Brett Smith for redOrbit.com - Your Universe Online
Within a span of three minutes, a star in the Usra Major constellation less than 16 light-years from Earth gave off a massive flare, making the object 15 times brighter than normal, according to a new report in the journal Astrophysics.
The star, known as WX“¯UMa, is a so-called flare star, a class of stars which can become 100 times or more brighter within a few seconds or minutes. These flares appear to be randomly occurring, and the stars return to their normal state tens of minutes after the event.
“We recorded a strong flare of the star WX“¯UMa, which became almost 15“¯times brighter in a matter of 160“¯seconds,” said report co-author Vakhtang Tamazian, an astrophysicist at the University of Santiago de Compostela.
WX UMa is part of a binary system with a companion star that shines almost 100“¯times brighter, except during WX“¯UMa flare events. The event described in the report was observed from the Byurakan Observatory in Armenia.
“During this period of less than three minutes the star underwent an abrupt change “¦ from a temperature of 2,800“¯kelvin to six or seven times more than that,” Tamazian noted.
While scientists currently do not know how to predict these flares, they do know how they develop.
“For some reason a small focus of instability arises within the plasma of the star, which causes turbulence in its magnetic field,” Tamazian explained. “A magnetic reconnection then occurs, a conversion of energy from the magnetic field into kinetic energy, in order to recover the stability of the flow, much like what happens in an electric discharge.”
Kinetic energy in the plasma then transforms into thermal energy in the upper layers of the star´s atmosphere. The resulting jump in temperature and brightness allows astrophysicists to see changes in the radiation spectrum.
“Photometric and spectroscopic monitoring of this kind of flare stars is very relevant because it provides us with information about the changing states and physical processes, which are in turn key to studying the formation and evolution of stars,” Tamazian said.
He added that in binary systems “observation of flares acquires a special importance, because we can investigate whether there is any relation between the frequency of flares and the position of the pair of stars on their orbit, a question which remains open.”
Flare stars are weak by nature and can only be seen from Earth if they are located relatively close, up to a distance of a few tens of light years. The solar system´s closest neighbor Proxima Centauri is actually a flare star capable of producing random bursts of energy. Just over four light-years away, Proxima Centauri is a red dwarf star that was discovered in 1915 by Robert Innes.
Most flare stars are fairly cool red dwarfs, with a surface temperature of less than 4,000 degrees Kelvin, compared to the Sun´s surface temperature of approximately 5,800 Kelvin. Recent research has suggested that even smaller brown dwarfs might be capable of producing flares.
Watch a digital animation of a flare star.