Only with the Hubble Space Telescope could we get such a brilliant view of our closest stellar neighbor: Proxima Centauri. Located in the constellation of Centaurus (The Centaur), Proxima is just slightly over four light years distant from Earth. Even though this recent Hubble image makes the tiny star appear bright, it really isn't. At around magnitude 11, it's barely visible to an average telescope - let alone the unaided eye!
So what makes this diminutive star special, other than the fact that it's the closest star to our Sun? In this case, it's the type. While Proxima Centauri has an extremely low average luminosity and is physically small compared to other stars (about 1/8th the mass of our Sun) it is what's known as a "flare star". This unusual stellar orb doesn't "burn" like others - it heats by the convection process - where the energy is physically moved up from the interior to the exterior, rather than radiated. As a result, the left-over hydrogen ash doesn't collect at the core... rather it circulates throughout the star. In the end, this means that Proxima will almost completely exhaust its nuclear fuel before the fusion of hydrogen comes to an end.
Proxima Centauri - Credit: ESA/Hubble & NASA
Not only is the life of a flare star unusual, but so are its appearances. Because of the convection process, Proxima is noted for drastic changes in brightness which can occur with no warning or pattern. Astronomers predict that stars such as Proxima will remain a main sequence member for around another four trillion years - or 300 times the age of the Universe as we know it!
Proxima was discovered in 1915 by Scottish astronomer Robert Innes, Director of the Union Observatory in Johannesburg, South Africa. At the time, he didn't know that it was the nearest star to Earth, only that it had the same proper motion as Alpha Centauri. Its name means "the closest," and while it applied to companion star, Alpha, it would be a name that would ring even more true when Dutch astronomer Joan Voute measured the star's trigonometric parallax and determined that Proxima Centauri was approximately the same distance from the Sun as Alpha. It has been the closest star to the Sun for about 32,000 years and will be so for about another 33,000 years!
Proxima Centauri is actually part of a triple star system ? its two companions, Alpha Centauri A and B, lie out of frame. However, they aren't the only ones sharing the same address. Six single stars, two binary star systems, and a triple star share a common motion through space with Proxima Centauri and the Alpha Centauri system. While it hasn't been proven yet, chances are they are all part of a moving group, similar to the Ursa Major System. Did these stars have a common point of origin? It's possible they may have all once belonged to a star cluster... a theory which will last at least until Proxima is shown not to be gravitationally bound to its companions!
About Tammy Plotner - Tammy is a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She's received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.