http://en.wikipedia.org/wiki/Proxima_Centauri wrote:
<<Proxima
Centauri's mass is about an eighth of the Sun's, and its average density is about 40 times that of the Sun. Although it has a very low average luminosity, Proxima is a flare star that undergoes random dramatic increases in brightness because of magnetic activity. The star's magnetic field is created by convection throughout the stellar body, and the resulting flare activity generates a total X-ray emission similar to that produced by the Sun. The mixing of the fuel at Proxima
Centauri's core through convection and the star's relatively low energy production rate suggest that it will be a main-sequence star for another four trillion years, or nearly 300 times the current age of the universe.
Searches for companions orbiting Proxima
Centauri have been unsuccessful, ruling out the presence of brown dwarfs and supermassive planets. Precision radial velocity surveys have also ruled out the presence of super-Earths within the star's habitable zone. The detection of smaller objects will require the use of new instruments, such as the proposed James Webb Space Telescope. Since Proxima
Centauri is a red dwarf and a flare star, whether a planet orbiting this star could support life is disputed. Nevertheless, because of the star's proximity to Earth, it has been proposed as a destination for interstellar travel.
Based on the parallax of 768.7 ± 0.3 milliarcseconds, measured using the Fine Guidance Sensors on the Hubble Space Telescope, Proxima
Centauri is roughly 4.2 light years from Earth, or 270,000 times more distant than the Sun. From Earth's vantage point, Proxima is separated by 2.18° from
Alpha Centauri, or four times the angular diameter of the full Moon. Proxima also has a relatively large proper motion—moving 3.85 arcseconds per year across the sky. It has a radial velocity toward the Sun of 21.7 km/s.
Among the known stars, Proxima
Centauri has been the closest star to the Sun for about 32,000 years and will be so for about another 33,000 years, after which the closest star to the Sun will be Ross 248. In 2001, J. García-Sánchez et al. predicted that Proxima will make its closest approach to the Sun, coming within 3.11 light years of the latter, in approximately 26,700 years. A 2010 study by V. V. Bobylev predicted a closest approach distance of 2.90 ly in about 27,400 years. Proxima
Centauri is orbiting through the Milky Way at a distance from the galactic core that varies from 8.3 to 9.5 kpc, and with an orbital eccentricity of 0.07.
From the time of the discovery of Proxima, it was suspected to be a true companion of the
Alpha Centauri binary star system. At a distance to
Alpha Centauri of just 0.21 ly (15,000 ± 700 astronomical units [AU]), Proxima
Centauri may be in orbit around
Alpha Centauri, with an orbital period of the order of 500,000 years or more. For this reason, Proxima is sometimes referred to as
Alpha Centauri C. Modern estimates, taking into account the small separation between and relative velocity of the stars, suggest that the chance of the observed alignment being a coincidence is roughly one in a million. Data from the Hipparcos satellite, combined with ground-based observations, is consistent with the hypothesis that the three stars are truly a bound system. If so, Proxima would currently be near apastron, the farthest point in its orbit from the
Alpha Centauri system. More accurate measurement of the radial velocity is needed to confirm this hypothesis.
If Proxima was bound to the
Alpha Centauri system during its formation, the stars would be likely to share the same elemental composition. The gravitational influence of Proxima may also have stirred up the
Alpha Centauri protoplanetary disks. This would have increased the delivery of volatiles such as water to the dry inner regions. Any terrestrial planets in the system may have been enriched by this material.
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. The space velocities of these stars are all within 10 km/s of
Alpha Centauri's peculiar motion. Thus, they may form a moving group of stars, which would indicate a common point of origin, such as in a star cluster. If it is determined that Proxima
Centauri is not gravitationally bound to
Alpha Centauri, then such a moving group would help explain their relatively close proximity.>>