Barnard's Star
 The location of Barnard's Star, c. 2006 (south is up) | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Ophiuchus |
| Pronunciation | /ˈbɑːrnərdz/ |
| Right ascension | 17h 57m 48.49803s[1] |
| Declination | +04° 41′ 36.2072″[1] |
| Apparent magnitude (V) | 9.511[2] |
| Characteristics | |
| Spectral type | M4.0V[3] |
| Apparent magnitude (U) | 12.497[2] |
| Apparent magnitude (B) | 11.240[2] |
| Apparent magnitude (R) | 8.298[2] |
| Apparent magnitude (I) | 6.741[2] |
| Apparent magnitude (J) | 5.24[4] |
| Apparent magnitude (H) | 4.83[4] |
| Apparent magnitude (K) | 4.524[4] |
| U−B color index | 1.257[2] |
| B−V color index | 1.713[2] |
| V−R color index | 1.213[2] |
| R−I color index | 1.557[2] |
| Variable type | BY Draconis[5] |
| Astrometry | |
| Radial velocity (Rv) | −110.6 ± 0.2[6] km/s |
| Proper motion (μ) | RA: −802.803[7] mas/yr Dec.: 10362.542[7] mas/yr |
| Parallax (π) | 546.9759 ± 0.0401[8] mas |
| Distance | 5.9629 ± 0.0004 ly (1.8282 ± 0.0001 pc) |
| Absolute magnitude (MV) | 13.21[2] |
| Details | |
| Mass | 0.144[6] M☉ |
| Radius | 0.196 ± 0.008[9] R☉ |
| Luminosity (bolometric) | 0.0035[10] L☉ |
| Luminosity (visual, LV) | 0.0004[10] L☉ |
| Temperature | 3,134 ± 102[10] K |
| Metallicity | 10–32% Sun[3]: 820 |
| Rotation | 130.4 d[11] |
| Age | ≈ 10[12] Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
| ARICNS | data |
  Barnard's Star Location of Barnard's Star in the constellation Ophiuchus | |
Barnard's Star /ˈbɑːrnərdz/ is a red dwarf about six light-years from Earth in the constellation of Ophiuchus. It is the fourth-nearest-known individual star to the Sun after the three components of the Alpha Centauri system, and the closest star in the northern celestial hemisphere.[16] Its stellar mass is about 14% of the Sun's. Despite its proximity, the star has a dim apparent magnitude of +9.5 and is invisible to the unaided eye; it is much brighter in the infrared than in visible light.
The star is named after the American astronomer E. E. Barnard,[17] who in 1916 measured its proper motion as 10.3 arcseconds per year relative to the Sun, the highest known for any star. The star had previously appeared on Harvard University photographic plates in 1888 and 1890.[18]
Barnard's Star is among the most studied red dwarfs because of its proximity and favorable location for observation near the celestial equator.[10] Historically, research on Barnard's Star has focused on measuring its stellar characteristics, its astrometry, and also refining the limits of possible extrasolar planets. Although Barnard's Star is ancient, it still experiences star flare events, one being observed in 1998.
From the early 1960s to the early 1970s, Peter van de Kamp argued that planets orbited Barnard's star. His specific claims of large gas giants were refuted in the mid-1970s after much debate.
In November 2018, a candidate super-Earth planetary companion known as Barnard's Star b was reported to orbit Barnard's Star. It was believed to have a minimum of 3.2 MEarth (Earth masses) and orbit at 0.4 AU.[19] However, work presented in July 2021 cast doubts upon the existence of this planet.[20]
Naming[]
In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[21] to catalogue and standardize proper names for stars. The WGSN approved the name Barnard's Star for this star on 1 February 2017 and it is now included in the List of IAU-approved Star Names.[22]
Description[]
Barnard's Star is a red dwarf of the dim spectral type M4, and it is too faint to see without a telescope. Its apparent magnitude is 9.5.
At 7–12 billion years of age, Barnard's Star is considerably older than the Sun, which is 4.5 billion years old, and it might be among the oldest stars in the Milky Way galaxy.[12] Barnard's Star has lost a great deal of rotational energy, and the periodic slight changes in its brightness indicate that it rotates once in 130 days[11] (the Sun rotates in 25). Given its age, Barnard's Star was long assumed to be quiescent in terms of stellar activity. In 1998, astronomers observed an intense stellar flare, showing that Barnard's Star is a flare star.[23] Barnard's Star has the variable star designation V2500 Ophiuchi. In 2003, Barnard's Star presented the first detectable change in the radial velocity of a star caused by its motion. Further variability in the radial velocity of Barnard's Star was attributed to its stellar activity.[24]
The proper motion of Barnard's Star corresponds to a relative lateral speed of 90 km/s. The 10.3 arcseconds it travels in a year amount to a quarter of a degree in a human lifetime, roughly half the angular diameter of the full Moon.[17]
The radial velocity of Barnard's Star towards the Sun is measured from its blueshift to be −110 km/s. Combined with its proper motion, this gives a space velocity (actual velocity relative to the Sun) of −142.6 ± 0.2 km/s. Barnard's Star will make its closest approach to the Sun around 11,800 CE, when it will approach to within about 3.75 light-years.[6]
Proxima Centauri is the closest star to the Sun at a position currently 4.24 light-years distant from it. However, despite Barnard's Star's even closer pass to the Sun in 11,800 CE, it will still not then be the nearest star, since by that time Proxima Centauri will have moved to a yet-nearer proximity to the Sun.[25] At the time of the star's closest pass by the Sun, Barnard's Star will still be too dim to be seen with the naked eye, since its apparent magnitude will only have increased by one magnitude to about 8.5 by then, still being 2.5 magnitudes short of visibility to the naked eye.
Barnard's Star has a mass of about 0.14 solar masses (M☉),[6] and a radius 0.2 times that of the Sun.[10][26] Thus, although Barnard's Star has roughly 150 times the mass of Jupiter (MJ), its radius is only roughly 2 times larger, due to its much higher density. Its effective temperature is 3,100 kelvin, and it has a visual luminosity of 0.0004 solar luminosities.[10] Barnard's Star is so faint that if it were at the same distance from Earth as the Sun is, it would appear only 100 times brighter than a full moon, comparable to the brightness of the Sun at 80 astronomical units.[27]
Barnard's Star has 10–32% of the solar metallicity.[3] Metallicity is the proportion of stellar mass made up of elements heavier than helium and helps classify stars relative to the galactic population. Barnard's Star seems to be typical of the old, red dwarf population II stars, yet these are also generally metal-poor halo stars. While sub-solar, Barnard's Star's metallicity is higher than that of a halo star and is in keeping with the low end of the metal-rich disk star range; this, plus its high space motion, have led to the designation "intermediate population II star", between a halo and disk star.[3][24] Although some recently published scientific papers have given much higher estimates for the metallicity of the star, very close to the Sun's level, between 75 and 125% of the solar metallicity.[28][29]
Planetary system[]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b (disputed[20]) | ≥3.23±0.44 M
|