Flare star becomes 15 times brighter in less than 3 minutes

Astrophysicists 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, spotted by astrophysicists at the University of Santiago de Compostela (Spain) and the Byurakan Observatory (Armenia), 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,” astrophysicist Vakhtang Tamazian, professor at the University of Santiago de Compostela explained to SINC.

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,” he stated.

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. 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,” explained Tamazian.

Next, kinetic energy in the plasma transforms into thermal energy in the upper layers of the atmosphere and the star’s corona. This significant rise in the temperature and brightness of the star enables astronomers to detect changes in the radiation spectrum.

The finding has been published in the Astrophysics journal.