Companion: Proxima Centauri
The much fainter red dwarf star named Proxima Centauri, or simply Proxima, is about 15,000 AU away from Alpha Centauri AB. This is equivalent to 0.24 light years or 2.2 trillion kilometres—about 5% the distance between the Sun and Alpha Centauri AB. Proxima may be gravitationally bound to Alpha Centauri AB, orbiting it with a period between 100,000 and 500,000 years. However, it is also possible that Proxima is not gravitationally bound and thus is moving along a hyperbolic trajectory around Alpha Centauri AB. The main evidence for a bound orbit is that Proxima's association with Alpha Centauri AB is unlikely to be accidental, since they share approximately the same motion through space. Theoretically, Proxima could leave the system after several million years. It is not yet certain whether Proxima and Alpha are truly gravitationally bound.
Proxima is an M5.5 V spectral class red dwarf with an absolute magnitude of +15.53, which is only a small fraction of the Sun's luminosity. By mass, Proxima is presently calculated as 0.123 ± 0.06 M☉ (rounded to 0.12 M☉) or about one-eighth that of the Sun.
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