Proxima Centauri
Coordinates: 
14h 29m 42.9487s, −62° 40′ 46.141″
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Centaurus |
| Pronunciation | /ˌprɒksəmə sɛnˈtɔːri/ or /ˈprɒksɪmə sɛnˈtɔːraɪ/[1] |
| Right ascension | 14h 29m 42.94853s[2] |
| Declination | −62° 40′ 46.1631″[2] |
| Apparent magnitude (V) | 10.43 – 11.11[3] |
| Characteristics | |
| Evolutionary stage | Main sequence (red dwarf) |
| Spectral type | M5.5Ve[4] |
| Apparent magnitude (U) | 14.21[5] |
| Apparent magnitude (B) | 12.95[5] |
| Apparent magnitude (V) | 11.13[5] |
| Apparent magnitude (R) | 9.45[5] |
| Apparent magnitude (I) | 7.41[5] |
| Apparent magnitude (J) | 5.357±0.023[6] |
| Apparent magnitude (H) | 4.835±0.057[6] |
| Apparent magnitude (K) | 4.384±0.033[6] |
| U−B color index | 1.26 |
| B−V color index | 1.82 |
| V−R color index | 1.68 |
| R−I color index | 2.04 |
| J−H color index | 0.522 |
| J−K color index | 0.973 |
| Variable type | UV Ceti ("flare star")[3] |
| Astrometry | |
| Radial velocity (Rv) | −22.204±0.032[7] km/s |
| Proper motion (μ) | RA: −3781.741[8] mas/yr Dec.: 769.465[8] mas/yr |
| Parallax (π) | 768.0665 ± 0.0499[8] mas |
| Distance | 4.2465 ± 0.0003 ly (1.30197 ± 0 pc) |
| Absolute magnitude (MV) | 15.60[9] |
| Orbit[7] | |
| Primary | Alpha Centauri AB |
| Companion | Proxima Centauri |
| Period (P) | 547000+6600 −4000 yr |
| Semi-major axis (a) | 8700+700 −400 AU |
| Eccentricity (e) | 0.50+0.08 −0.09 |
| Inclination (i) | 107.6+1.8 −2.0° |
| Longitude of the node (Ω) | 126±5° |
| Periastron epoch (T) | +283+59 −41 |
| Argument of periastron (ω) (secondary) | 72.3+8.7 −6.6° |
| Details | |
| Mass | 0.1221±0.0022[7] M☉ |
| Radius | 0.1542±0.0045[7] R☉ |
| Luminosity (bolometric) | 0.0017[10] L☉ |
| Luminosity (visual, LV) | 0.00005[nb 1] L☉ |
| Surface gravity (log g) | 5.20±0.23[11] cgs |
| Temperature | 3042±117[11] K |
| Metallicity [Fe/H] | 0.21[12][nb 2] dex |
| Rotation | 82.6±0.1[15] days |
| Rotational velocity (v sin i) | < 0.1[15] km/s |
| Age | 4.85[16] Gyr |
| Other designations | |
Alf Cen C, Alpha Centauri C, V645 Centauri, GJ 551, HIP 70890, CCDM J14396-6050C, LFT 1110, LHS 49, LPM 526, LTT 5721, NLTT 37460[17] | |
| Database references | |
| SIMBAD | data |
| ARICNS | data |
Proxima Centauri is a small, low-mass star located 4.2465 light-years (1.3020 pc) away from the Sun in the southern constellation of Centaurus. Its Latin name means the 'nearest [star] of Centaurus'. It was discovered in 1915 by Robert Innes and is the nearest-known star to the Sun. With a quiescent apparent magnitude 11.13, it is too faint to be seen with the unaided eye. Proxima Centauri is a member of the Alpha Centauri star system, being identified as component Alpha Centauri C, and is 2.18° to the southwest of the Alpha Centauri AB pair. It is currently 12,950 AU (0.2 ly) from AB, which it orbits with a period of about 550,000 years.
Proxima Centauri is a red dwarf star with a mass about 12.5% of the Sun's mass (M☉), 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 (14%) 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 thorough 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 confirmed exoplanets: Proxima Centauri b and Proxima Centauri c. Proxima Centauri b orbits the star at a distance of roughly 0.05 AU (7.5 million km) with an orbital period of approximately 11.2 Earth days. Its estimated mass is at least 1.17 times that of Earth.[18] Proxima b is orbiting 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, its habitability is disputed. A super-Earth, Proxima Centauri c, orbits roughly 1.5 AU (220 million km) away every 1,900 d (5.2 yr).[19][20] A faint additional signal was detected in a 2019 exoplanet search using radial velocity data, with a period of 5.15 days. Possible explanations for the signal include undiscovered exoplanets or statistical noise.[18][nb 3]
Observation[]
In 1915, the Scottish astronomer Robert Innes, director of the Union Observatory in Johannesburg, South Africa, discovered a star that had the same proper motion as Alpha Centauri.[22][23][24][25] He suggested that it be named Proxima Centauri[26] (actually Proxima Centaurus).[27] In 1917, at the Royal Observatory at the Cape of Good Hope, the Dutch astronomer Joan Voûte measured the star's trigonometric parallax at 0.755″±0.028″ and determined that Proxima Centauri was approximately the same distance from the Sun as Alpha Centauri. It was also found to be the lowest-luminosity star known at the time.[28] An equally accurate parallax determination of Proxima Centauri was made by American astronomer Harold L. Alden in 1928, who confirmed Innes's view that it is closer, with a parallax of 0.783″±0.005″.[23][26]
In 1951, American astronomer Harlow Shapley announced that Proxima Centauri is a flare star. Examination of past photographic records showed that the star displayed a measurable increase in magnitude on about 8% of the images, making it the most active flare star then known.[31][32] The proximity of the star allows for detailed observation of its flare activity. In 1980, the Einstein Observatory produced a detailed X-ray energy curve of a stellar flare on Proxima Centauri. Further observations of flare activity were made with the EXOSAT and ROSAT satellites, and the X-ray emissions of smaller, solar-like flares were observed by the Japanese ASCA satellite in 1995.[33] Proxima Centauri has since been the subject of study by most X-ray observatories, including XMM-Newton and Chandra.[34]
In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars.[35] The WGSN approved the name Proxima Centauri for this star on August 21, 2016, and it is now so included in the List of IAU approved Star Names.[36]
Because of Proxima Centauri's southern declination, it can only be viewed south of latitude 27° N.[nb 4] Red dwarfs such as Proxima Centauri are too faint to be seen with the naked eye. Even from Alpha Centauri A or B, Proxima would only be seen as a fifth magnitude star.[37][38] It has apparent visual magnitude 11, so a telescope with an aperture of at least 8 cm (3.1 in) is needed to observe it, even under ideal viewing conditions—under clear, dark skies with Proxima Centauri well above the horizon.[39]
In 2016, a superflare was observed from Proxima Centauri, the strongest flare ever seen. The optical brightness increased by a factor of 68× to approximately magnitude 6.8. It is estimated that similar flares occur around five times every year but are of such short duration, just a few minutes, that they have never been observed before.[29]
On 2020 April 22 and 23, the New Horizons spacecraft took images of two of the nearest stars, Proxima Centauri and Wolf 359. When compared with Earth-based images, a very large parallax effect was easily visible. However, this was mostly useful for illustrative purposes and did not improve on previous distance measurements.[40][41]
Physical properties[]
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. M5.5 means that it falls in the low-mass end of M-type dwarf stars.[16] Its absolute visual magnitude, or its visual magnitude as viewed from a distance of 10 parsecs (33 ly), is 15.5.[42] Its total luminosity over all wavelengths is 0.17% that of the Sun,[10] although when observed in the wavelengths of visible light the eye is most sensitive to, it is only 0.0056% as luminous as the Sun.[43] More than 85% of its radiated power is at infrared wavelengths.[44]
In 2002, optical interferometry with the Very Large Telescope (VLTI) found that the angular diameter of Proxima Centauri is 1.02±0.08 mas. 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 12.2% M☉, or 129 Jupiter masses (MJ).[45] The mass has been calculated directly, although with less precision, from observations of microlensing events to be 0.150+0.062
−0.051 M☉.[46]
Lower mass main-sequence stars have higher mean density than higher mass ones,[47] and Proxima Centauri is no exception: it has a mean density of 47.1×103 kg/m3 (47.1 g/cm3), compared with the Sun's mean density of 1.411×103 kg/m3 (1.411 g/cm3).[nb 5] The measured surface gravity of Proxima Centauri, given as the base-10 logarithm of the acceleration in units of cgs, is 5.20.[11] This is 162 times the surface gravity on Earth.[nb 6]
A 1998 study of photometric variations indicates that Proxima Centauri rotates once every 83.5 days.[48] A subsequent time series analysis of chromospheric indicators in 2002 suggests a longer rotation period of 116.6±0.7 days.[49] This was subsequently ruled out in favor of a rotation period of 82.6±0.1 days.[15]
Because of its low mass, the interior of the star is completely convective,[50] 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 after about 4 trillion years.[51]
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)[52] increase the overall luminosity of the star. On May 1, 2019, an extreme flare event briefly became the brightest ever detected, with a far ultraviolet emission of 2×1030 erg.[53] These flares can grow as large as the star and reach temperatures measured as high as 27 million K[34]—hot enough to radiate X-rays.[54] Proxima Centauri's quiescent X-ray luminosity, approximately (4–16) × 1026 erg/s ((4–16) × 1019 W), is roughly equal to that of the much larger Sun. The peak X-ray luminosity of the largest flares can reach 1028 erg/s (1021 W).[34]
Proxima Centauri's chromosphere is active, and its spectrum displays a strong emission line of singly ionized magnesium at a wavelength of 280 nm.[55] 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,[56] and its total X-ray emission is comparable to the sun's.[57] Proxima Centauri's overall activity level is considered low compared to other red dwarfs,[57] which is consistent with the star's estimated age of 4.85 × 109 years,[16] since the activity level of a red dwarf is expected to steadily wane over billions of years as its stellar rotation rate decreases.[58] The activity level also appears to vary[59] with a period of roughly 442 days, which is shorter than the solar cycle of 11 years.[60]
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 solar surface.[61]
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 (L☉) and warming up any orbiting bodies for a period of several billion years. When the hydrogen fuel is exhausted, Proxima Centauri will then evolve into a white dwarf (without passing through the red giant phase) and steadily lose any remaining heat energy.[51]
Distance and motion[]
Based on a parallax of 768.0665±0.0499 mas, published in 2020 in Gaia Data Release 3, Proxima Centauri is 4.2465 light-years (1.3020 pc; 268,550 AU) from the Sun.[8] Previously published parallaxes include: 768.5±0.2 mas in 2018 by Gaia DR2, 768.13±1.04 mas, in 2014 by the Research Consortium On Nearby Stars;[62] 772.33±2.42 mas, in the original Hipparcos Catalogue, in 1997;[63] 771.64±2.60 mas in the Hipparcos New Reduction, in 2007;[2] and 768.77±0.37 mas using the Hubble Space Telescope's fine guidance sensors, in 1999.[9] From Earth's vantage point, Proxima Centauri is separated from Alpha Centauri by 2.18 degrees,[64] or four times the angular diameter of the full Moon.[65] Proxima Centauri also has a relatively large proper motion—moving 3.85 arcseconds per year across the sky.[66] It has a radial velocity toward the Sun of 22.2 km/s.[7]
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 3.11 ly (0.95 pc).[67] A 2010 study by V. V. Bobylev predicted a closest approach distance of 2.90 ly (0.89 pc) in about 27,400 years,[68] followed by a 2014 study by C. A. L. Bailer-Jones predicting a perihelion approach of 3.07 ly (0.94 pc) in roughly 26,710 years.[69] Proxima Centauri is orbiting through the Milky Way at a distance from the Galactic Centre that varies from 27 to 31 kly (8.3 to 9.5 kpc), with an orbital eccentricity of 0.07.[70]
Ever since the discovery of Proxima Centauri, it has been suspected to be a true companion of the Alpha Centauri binary star system. Data from the Hipparcos satellite, combined with ground-based observations, were consistent with the hypothesis that the three stars are a bound system. For this reason, Proxima Centauri is sometimes referred to as Alpha Centauri C. Kervella et al. (2017) used high-precision radial velocity measurements to determine with a high degree of confidence that Proxima and Alpha Centauri are gravitationally bound.[7] Proxima Centauri's orbital period around the Alpha Centauri AB barycenter is 547000+6600
−4000 years with an eccentricity of 0.5±0.08; it approaches Alpha Centauri to 4300+1100
−900 AU at periastron and retreats to 13000+300
−100 AU at apastron.[7] At present, Proxima Centauri is 12,947 ± 260 AU (1.94 ± 0.04 trillion km) from the Alpha Centauri AB barycenter, nearly to the farthest point in its orbit.[7]
Such a triple system can form naturally through a low-mass star being dynamically captured by a more massive binary of 1.5–2 M☉ within their embedded star cluster before the cluster disperses.[71] However, more accurate measurements of the radial velocity are needed to confirm this hypothesis.[72] 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 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, so possibly enriching any terrestrial planets in the system with this material.[72] 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.[14]
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,[73] such as in a star cluster.
Planetary system[]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| d (unconfirmed) | ≥ 0.29±0.08 M
|