The flare star WX UMa becomes 15 times brighter in 160 seconds

A flare star. Credit: Casey Reed /NASA

Astrophysicists at the University of Santiago de Compostela Spain and the Byurakan Observatory (Armenia) have detected a star of low luminosity which within a matter of moments gave off a flare so strong that it became almost 15 times brighter.

The star in question is the flare star WX UMa.

"We recorded a strong flare of the star WX UMa, which became almost 15 times brighter in a matter of 160 seconds," explains the astrophysicist Vakhtang Tamazian, professor at the University of Santiago de Compostela. The finding has been published in the 'Astrophysics' journal.

This star is in the Ursa Major constellation, around 15.6 light years from the Earth, and it forms part of a binary system.

Its companion shines almost 100 times brighter, except at times such as that observed, in which the WX UMa gives off its flares. This can happen several times a year, but not as strongly as that which was recorded in this instance.

Dr Tamazian and other researchers detected this exceptional brightness from the Byurakan Observatory in Armenia.

"Furthermore, during this period of less than three minutes the star underwent an abrupt change from spectral type M to B; in other words, it went from a temperature of 2,800 kelvin (K) to six or seven times more than that."

Based on their spectral absorption lines, stars are classified using letters. Type M stars have a surface temperature of between 2,000 and 3,700 K; Type B between 10,000 and 33,000 K.

WX UMa belongs to the limited group of "flare stars", a class of variable stars which exhibit increases in brightness of up to 100 factors or more within a matter of seconds or minutes.

These increases are sudden and irregular – practically random, in fact. They then return to their normal state within tens of minutes.

Scientists do not know how this flaring arises, but they know how it develops: "For some reason a small focus of instability arises within the plasma of the star, which causes turbulence in its magnetic field," explains Tamazian.

"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."

More information: N. D. Melikian, V. S. Tamazian, R. Sh. Natsvlishvili, A. A. Karapetian. "Spectral observations of flare stars in the neighborhood of the Sun". Astrophysics 56 (1): 8-18, March 2013. link.springer.com/article/10.1007%2Fs10511-013-9263-z