Talk about a celestial mood swing: Scientists using the SCORPIO camera of the Byurakan Astrophysical Observatory recently watched as a low luminosity star suddenly burst to life in an extraordinarily short amount of time — becoming 15 times brighter in less than three minutes.
Star WX UMa, which is relatively close-by in the Ursa-major constellation, is about 15.6 light-years from Earth and is part of a binary system. It's a flare star — a normally subdued low luminosity object that occassionally and unpredicably boosts its brightness and heat in a matter of seconds. But it's an effect that doesn't last long. The stars return back to their normal state in about 10 minutes.
Fascinatingly, the effect is so dramatic that the classification of the star literally changes within a few seconds. In this case, WX UMa temporarily transformed from spectral type M to B. Its temperature went from about 2,800 kelvin (K) to six or seven times that — somewhere between 10,000 to 33,000 K.
These flares happen when instability within the plasma of the star 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," said a researcher when speaking to SINC. This kinetic energy transforms into thermal energy in the upper layers of the atmosphere and the star's corona, driving up its temperature and brightness.
Read the entire study at Astrophysics: "Spectral observations of flare stars in the neighborhood of the sun."
Image: Casey Reed/NASA.