THE FLARE STAR WX UMA BECOMES 15 TIMES BRIGHTER IN LESS THAN THREE MINUTES
Phys.org
June 14 2013
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 to SINC
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.”