BO Microscopii
Encyclopedia
BO Microscopii is a star in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

 Microscopium
Microscopium
Microscopium is a small constellation in the southern sky, created in the 18th century by Nicolas Louis de Lacaille. Its name is Latin for microscope. Its stars are very faint and hardly visible from most of the non-tropical northern hemisphere.-References:...

 located about 170 light years from the Sun. It has been dubbed "Speedy Mic" because of the ultra-rapid rotation rate. The projected rotational velocity
Stellar rotation
Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface....

 at the equator of this star is about 135 km/s, which, with an estimated inclination of 70° to the line of sight from the Earth, means it completes a rotation every . The photosphere of this star shows a high level of magnetic activity, with multiple star spots and prominences observed at the same time. As many as 25 prominences have been observed simultaneously, extending outward as far as 3.6 times the radius of the star. BO Mic is a flare star
Flare star
A flare star is a variable star that can undergo unpredictable dramatic increases in brightness for a few minutes. It is believed that the flares on flare stars are analogous to solar flares in that they are due to magnetic reconnection in the atmospheres of the stars. The brightness increase is...

that undergoes sudden increases in X-ray and ultraviolet emissions. These events can emit a hundred times more energy than large solar flares. Speedy Mic is one of the most active stars in the vicinity of the Sun.
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