Proxima Centauri is the nearest star to Earth after the Sun, located 4.25 light-years (1.3 parsecs) away in the southern constellation of Centaurus. Discovered in 1915 by Robert Innes, it is a small, low-mass star, too faint to be seen with the naked eye, with an apparent magnitude of 11.13. Proxima Centauri is a member of the Alpha Centauri star system, being identified as component Alpha Centauri C, and is 2.18° southwest of the Alpha Centauri AB pair. It is currently from AB, which it orbits with a period of about 550,000 years. Its Latin name means the 'nearest [star] of Centaurus'.
Proxima Centauri is a red dwarf star with a mass about 12.5% of the Sun's mass (), and average density about 33 times that of the Sun. Because of Proxima Centauri's proximity to Earth, its angular diameter can be measured directly. Its actual diameter is about one-seventh (15%) the diameter of the Sun. Although it has a very low average luminosity, Proxima Centauri is a flare star that randomly undergoes 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 internal mixing of its fuel by convection through its core and Proxima's relatively low energy-production rate, mean that it will be a main-sequence star for another four trillion years.
Proxima Centauri has two known exoplanets and one candidate exoplanet: Proxima Centauri b, Proxima Centauri d and the disputed Proxima Centauri c.Extrasolar planet names are designated following the International Astronomical Union's naming conventions in alphabetical order according to their respective dates of discovery, with 'Proxima Centauri a' being the star itself. Proxima Centauri b orbits the star at a distance of roughly with an orbital period of approximately 11.2 Earth days. Its estimated mass is at least 1.06 times that of Earth. Proxima b orbits within Proxima Centauri's habitable zone—the range where temperatures are right for liquid water to exist on its surface—but, because Proxima Centauri is a red dwarf and a flare star, the planet's habitability is highly uncertain. A sub-Earth, Proxima Centauri d, roughly away, orbits it every 5.1 days. A candidate sub-Neptune, Proxima Centauri c, roughly away from Proxima Centauri, orbits it every .
General characteristics
Proxima Centauri is a red dwarf, because it belongs to the main sequence on the Hertzsprung–Russell diagram and is of spectral class M5.5. The M5.5 class means that it falls in the low-mass end of M-type dwarf stars, with its hue shifted toward red-yellow by an effective temperature of . Its absolute visual magnitude, or its visual magnitude as viewed from a distance of , is 15.5. Its total luminosity over all wavelengths is only 0.16% that of the Sun, although when observed in the wavelengths of visible light to which the eye is most sensitive, it is only 0.0056% as luminous as the Sun. More than 85% of its radiated power is at infrared wavelengths.
In 2002, optical interferometry with the Very Large Telescope (VLTI) found that the angular diameter of Proxima Centauri is . Because its distance is known, the actual diameter of Proxima Centauri can be calculated to be about 1/7 that of the Sun, or 1.5 times that of Jupiter. The star's mass, estimated from stellar theory, is , or 129 Jupiter masses (). The mass has been calculated directly, although with less precision, from observations of microlensing events to be .
Lower mass main-sequence stars have higher mean density than higher mass ones, and Proxima Centauri is no exception: it has a mean density of , compared with the Sun's mean density of .The density (ρ) is given by the mass divided by the volume. Relative to the Sun, therefore, the density is = = = 4.71 kg/m3, where is the average solar density. See:
The measured surface gravity of Proxima Centauri, given as the base-10 logarithm of the acceleration in units of cgs, is 5.20. This is 162 times the surface gravity on Earth.The standard surface gravity on the Earth is , for a "log g" value of 2.992. The difference in logarithms is 5.20 − 2.99 = 2.21, yielding a multiplier of 102.21 = 162. For the Earth's gravity, see:
A 1998 study of photometric variations indicated that Proxima Centauri completes a full rotation once every 83.5 days. A subsequent time series analysis of chromospheric indicators in 2002 suggested a longer rotation period of days. Later observations of the star's magnetic field subsequently revealed that the star rotates with a period of days, consistent with a measurement of days from radial velocity observations; the most recent estimate as of 2026 is days. It is thought to rotate at an inclination of to the line of sight.
Structure and fusion Because of its low mass, the interior of the star is completely convective, causing energy to be transferred to the exterior by the physical movement of plasma rather than through radiative processes. This convection means that the helium ash left over from the thermonuclear fusion of hydrogen does not accumulate at the core but is instead circulated throughout the star. Unlike the Sun, which will only burn through about 10% of its total hydrogen supply before leaving the main sequence, Proxima Centauri will consume nearly all of its fuel before the fusion of hydrogen comes to an end.
Convection is associated with the generation and persistence of a magnetic field. The magnetic energy from this field is released at the surface through stellar flares that briefly (as short as per ten seconds) increase the overall luminosity of the star. On 6 May 2019, a flare event bordering Solar M and X flare class, briefly became the brightest ever detected, with a far ultraviolet emission of . These flares can grow as large as the star and reach temperatures measured as high as 27 million K—hot enough to radiate X-rays. Proxima Centauri's quiescent X-ray luminosity, approximately (4–16) erg/s ((4–16) W), is roughly equal to that of the much larger Sun. The peak X-ray luminosity of the largest flares can reach erg/s ( W).
Proxima Centauri's chromosphere is active, and its spectrum displays a strong emission line of singly ionized magnesium at a wavelength of 280 nm. About 88% of the surface of Proxima Centauri may be active, a percentage that is much higher than that of the Sun even at the peak of the solar cycle. Even during quiescent periods with few or no flares, this activity increases the corona temperature of Proxima Centauri to 3.5 million K, compared to the 2 million K of the Sun's corona, and its total X-ray emission is comparable to the sun's. Proxima Centauri's overall activity level is considered low compared to other red dwarfs, which is consistent with the star's estimated age of 4.85 years, since the activity level of a red dwarf is expected to steadily wane over billions of years as its stellar rotation rate decreases. The activity level appears to vary with a period of roughly 442 days, which is shorter than the Sun's solar cycle of 11 years.
Proxima Centauri has a relatively weak stellar wind, no more than 20% of the mass-loss rate of the solar wind. Because the star is much smaller than the Sun, the mass loss per unit surface area from Proxima Centauri may be eight times that from the Sun's surface.
Life phases
A red dwarf with the mass of Proxima Centauri will remain on the main sequence for about four trillion years. As the proportion of helium increases because of hydrogen fusion, the star will become smaller and hotter, gradually transforming into a so-called "blue dwarf". Near the end of this period it will become significantly more luminous, reaching 2.5% of the Sun's luminosity () and warming any orbiting bodies for a period of several billion years. When the hydrogen fuel is exhausted, Proxima Centauri will then evolve into a helium white dwarf (without passing through the red giant phase) and steadily lose any remaining heat energy.
The Alpha Centauri system may have formed through a low-mass star being dynamically captured by a more massive binary of within their embedded star cluster before the cluster dispersed. However, more accurate measurements of the radial velocity are needed to confirm this hypothesis. If Proxima Centauri was bound to the Alpha Centauri system during its formation, the stars are likely to share the same elemental composition. The gravitational influence of Proxima might have disturbed the Alpha Centauri protoplanetary disks. This would have increased the delivery of volatiles such as water to the dry inner regions, so possibly enriching any terrestrial planets in the system with this material.
Alternatively, Proxima Centauri may have been captured at a later date during an encounter, resulting in a highly eccentric orbit that was then stabilized by the galactic tide and additional stellar encounters. Such a scenario may mean that Proxima Centauri's planetary companions have had a much lower chance for orbital disruption by Alpha Centauri. As the members of the Alpha Centauri pair continue to evolve and lose mass, Proxima Centauri is predicted to become unbound from the system in around 3.5 billion years from the present. Thereafter, the star will steadily diverge from the pair.
Motion and location
Based on a parallax of , published in 2020 in Gaia Data Release 3, Proxima Centauri is from the Sun. Previously published parallaxes include: in 2018 by Gaia DR2, , in 2014 by the Research Consortium On Nearby Stars; , in the original Hipparcos Catalogue, in 1997; in the Hipparcos New Reduction, in 2007; and using the Hubble Space Telescope fine guidance sensors, in 1999. From Earth's vantage point, Proxima Centauri is separated from Alpha Centauri by 2.18 degrees, or four times the angular diameter of the full Moon. Proxima Centauri has a relatively large proper motion—moving 3.85 arcseconds per year across the sky. It has a radial velocity towards the Sun of 22.2 km/s. From Proxima Centauri, the Sun would appear as a bright 0.4-magnitude star in the constellation Cassiopeia, similar to Achernar or Procyon from Earth.The coordinates of the Sun would be diametrically opposite Proxima Centauri, at α=, δ=. The absolute magnitude Mv of the Sun is 4.83, so at a parallax π of 0.77199 the apparent magnitude m is given by 4.83 − 5(log10(0.77199) + 1) = 0.40. See: The star is located in the G-Cloud.
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 25,000 years, after which Alpha Centauri A and Alpha Centauri B will alternate approximately every 79.91 years as the closest star to the Sun. In 2001, J. García-Sánchez et al. predicted that Proxima Centauri will make its closest approach to the Sun in approximately 26,700 years, coming within . A 2010 study by V. V. Bobylev predicted a closest approach distance of in about 27,400 years, followed by a 2014 study by C. A. L. Bailer-Jones predicting a perihelion approach of in roughly 26,710 years. Proxima Centauri is orbiting through the Milky Way at a distance from the Galactic Centre that varies from , with an orbital eccentricity of 0.07.
Alpha Centauri