Flare stars are red dwarf stars that experience large fluctuations in surface temperature and solar flux. They are caused by solar flares and are highly unpredictable. When a flare star goes out, the surface temperature can rise from 3,000 K to 10,000 K within minutes. The closest star to Earth other than the Sun, Proxima Centauri, is a flare star.
Flare stars, also known as variable stars or UV Ceti variables, are red dwarf stars that experience large fluctuations in surface temperature and solar flux over the course of hours or even minutes. Flare stars are highly unpredictable, but amazing to watch, because most stars, such as those on the main sequence, experience the variability of their solar output only over millions of years of time.
Flare stars are caused by the equivalent of solar flares, except that they are much larger in size than the star. Because red dwarf stars have a mass of only a few tenths of the Sun, they have less gravity and flares are able to eject material more energetically from the star’s surface.
When a flare star goes out, the surface temperature can rise from 3,000 K to 10,000 K within minutes. These occur during magnetic reconnection events. The material a star is made of, plasma, responds to the magnetic fields generated by the star. Typically, plasma flow patterns are aligned with magnetic fields. Occasionally, magnetic fields collapse erratically to a lower energy state, drastically rearranging their configuration. The plasma rushes into the new configuration, colliding with itself and heating up thousands of degrees in the process. Because red dwarf stars are generally relatively cool, the huge burst of heat and energy is very noticeable. Some solar flares on flare stars are so large that they project 20% from the star’s surface relative to its diameter.
The closest star to Earth other than the Sun, Proxima Centauri, is a flare star. Because red dwarfs are inherently very faint, we can only observe those less than 50 light-years from Earth, so all flare stars are similarly close. The most famous is UV Ceti, discovered in 1948.
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