Star
Proxima Centauri is the nearest star to the Sun: an active red dwarf in the Alpha Centauri system, with a planet that illustrates the uncertainties of habitability.
Proxima Centauri, also catalogued as GJ 551, is the nearest star to the Sun. It lies about 4.2 light-years away in Centaurus, but its low luminosity makes it invisible to the unaided eye. It is a red dwarf. The M5.5 V classification adopted by Boyajian and colleagues describes a star considerably cooler than the Sun, not simply a smaller copy with identical conditions.
An apparent position near Alpha Centauri A and B was not enough to establish a physical association. A radial-velocity analysis reported by ESO in December 2016 supported Proxima being gravitationally bound to the pair, making a triple system. HARPS observations allowed the relative motion to be compared with the speed required to escape. Membership of Alpha Centauri is distinct from these stars all belonging to the Milky Way.
This profile retains the historical parameter set in Boyajian et al. (2012), Table 6: a radius of 0.141 ± 0.007 solar radii, an effective temperature of 3054 ± 79 K and a luminosity of 0.00155 ± 0.00002 solar luminosities. The radius was adopted from the interferometry of Demory et al. (2009); temperature and luminosity combine angular size, flux and distance. These are not new measurements from 2026, nor does effective temperature mean that every part of the star has the same temperature.
The adopted mass, 0.118 solar masses, comes from an empirical K-band mass–luminosity relation. The study assumes a 10% uncertainty, approximately 0.012 solar masses: it is not a direct interferometric mass measurement. The rounded distance of 4.2 light-years is an explanatory value, not a precision astrometric solution.
The Pale Red Dot campaign detected the periodic stellar motion behind the announcement of Proxima b in 2016, with an orbit of about 11.2 days. The team compared radial velocities and brightness changes to distinguish the planetary signal from stellar activity. Proxima flares, and its ultraviolet and X-ray radiation can influence the atmospheric evolution of a nearby planet.
An orbit within the habitable zone describes irradiation compatible with liquid water under certain assumptions. It does not establish the existence of oceans, an atmosphere or life. Radiation, temperature and planetary history must be considered together. This profile distinguishes the star from its planet and dates its sources: the 2016 discovery is not presented as current news.
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