Barnard's star
Encyclopedia
Barnard's Star, also known occasionally as Barnard's "Runaway" Star, is a very low-mass red dwarf
star
approximately six light-year
s away from Earth in the constellation
of Ophiuchus
(the Snake-holder). In 1916, the American astronomer
E.E. Barnard measured its proper motion
as 10.3 arcsecond
s per year, which remains the largest-known proper motion of any star relative to the Sun
. At a distance of about 1.8 parsecs from the Solar System
, or just under six light-years, Barnard's Star is the nearest known star in the constellation
Ophiuchus, and the fourth-closest known individual star to the Sun, after the three components of the Alpha Centauri
system. Despite its proximity, Barnard's Star, at a dim apparent magnitude
of about nine, is not visible with the unaided eye; however, it is much brighter in infrared light than it is in visible light.
Barnard's Star has been the subject of much study, and it has probably received more attention from astronomers than any other class M dwarf star due to its proximity and favorable location for observation near the celestial equator
. Historically, research on Barnard's Star has focused on measuring its stellar characteristics, its astrometry
, and also refining the limits of possible extrasolar planet
s. Although Barnard's Star is an ancient star, some observations suggest that it still experiences star flare
events.
Barnard's Star has also been the subject of some controversy. For a decade, from the early 1960s to the early 1970s, Peter van de Kamp
claimed that there was a gas giant
planet
(or planets) in orbit around it. While the presence of small terrestrial planets around the star remains a possibility, Van de Kamp's specific claims of large gas giant planets were refuted in the mid 1970s.
Barnard's Star is also notable as the target for Project Daedalus
, a study on the possibility of fast, unmanned travel to nearby star systems
.
M4, and it is too faint to see without a telescope
. Its apparent magnitude
is 9.54. This compares with a magnitude of −1.5 for Sirius
– the brightest star in the night sky – and about 6.0 for the faintest visible objects with the naked eye (this magnitude scale is logarithmic
, and so the magnitude of 9.54 is only about 1/27th of the brightness of the faintest star that can be seen with the naked eye under good viewing conditions).
At seven to 12 billion years of age, Barnard's Star is considerably older than the Sun, and it might be among the oldest stars in the Milky Way
galaxy. Barnard's Star has lost a great deal of rotational energy, and the periodic slight changes in its brightness indicate that it rotates just once every 130 days (compared with just over 25 days for the Sun). Given its age, Barnard's Star was long assumed to be quiescent in terms of stellar activity. However in 1998, astronomers observed an intense stellar flare, surprisingly showing that Barnard's Star is a flare star
. 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.
The proper motion of Barnard's Star corresponds to a relative lateral speed ("sideways" relative to our line of sight to the Sun) of 90 km/s. The 10.3 seconds of arc it travels annually amounts to a quarter of a degree in a human lifetime, roughly half the angular diameter of the full Moon.
The radial velocity of Barnard's Star towards the Sun can be measured by its blue shift
. Two measurements are given in catalogue
s: 106.8 km/s in SIMBAD
, which refers to a 1967 compilation of older measurements, and 110.8 km/s in ARICNS and similar values in all modern astronomical references. These measurements, combined with proper motion, suggest a true velocity relative to the Sun of 139.7 and 142.7 km/s, respectively. Barnard's Star will make its closest approach to the Sun around AD 11,700, when it approaches to within about 3.8 light-years. However, at that time, Barnard's Star will not be the nearest star, since Proxima Centauri
will have moved even closer to the Sun. Barnard's Star will still be too dim to be seen with the naked eye at the time of its closest approach, since its apparent magnitude will be about 8.5 then. After that it will gradually recede from the Sun.
Barnard's Star has approximately 17% of a solar mass
, and it has a radius 15% to 20% of that of the Sun. In 2003, its radius was estimated as 0.20±0.008 of the solar radius, at the high end of the ranges that were typically calculated in the past, indicating that previous estimates of the radius of Barnard's Star probably underestimated the actual value. Thus, although Barnard's Star has roughly 180 times the mass of Jupiter, its radius is only 1.5 to 2.0 times larger, reflecting the tendency of objects in the brown dwarf
range to be about the same size. Its effective temperature
is 3,134(±102) kelvin
, and it has a visual luminosity just 4/10,000ths of solar luminosity, corresponding to a bolometric luminosity of 34.6/10,000ths. 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 Unit
s.
In a broad survey of the metallicity
of M-class dwarf stars, Barnard's Star's was placed between −0.5 and −1.0 on the metallicity scale, which is roughly 10 to 32% of the value for the Sun. Metallicity, the proportion of stellar mass made up of elements heavier than helium
, 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 star
s. While sub-solar, Barnard's Star's metallicity is higher than 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.
that he had detected, by using astrometry, a perturbation in the proper motion
of Barnard's Star consistent with its having one or more planets comparable in mass with Jupiter
. Van de Kamp had been observing the star from 1938, attempting, with colleagues at the Swarthmore College
observatory, to find minuscule variations of one micrometre
in its position on photographic plates consistent with orbital perturbations (wobbles) in the star that would indicate a planetary companion; this involved as many as ten people averaging their results in looking at plates, to avoid systemic, individual errors. Van de Kamp's initial suggestion was a planet having about 1.6 the Jovian mass at a distance of 4.4 AU in a slightly eccentric orbit, and these measurements were apparently refined in a 1969 paper. Later that year, Van de Kamp suggested that there were two planets of 1.1 and 0.8 Jovian masses.
Other astronomers subsequently repeated Van de Kamp's measurements, and two important papers in 1973 undermined the claim of a planet or planets. George Gatewood and Heinrich Eichhorn, at a different observatory and using newer plate measuring techniques, failed to verify the planetary companion. Another paper published by John L. Hershey four months earlier, also using the Swarthmore observatory, found that changes in the astrometric field of various stars correlated to the timing of adjustments and modifications that had been carried out on the refractor telescope's objective lens; the planetary "discovery" was an artifact of maintenance and upgrade work. The affair has been discussed as part of a broader scientific review.
Van de Kamp never acknowledged any error and published a further confirmation of two planets' existence as late as 1982; he died in 1995. Wulff Heintz, Van de Kamp's successor at Swarthmore and an expert on double stars, questioned his findings and began publishing criticisms from 1976 onwards. The two men were reported to have become estranged from each other because of this.
in 1999. By refining the values of a star's motion, the mass and orbital boundaries for possible planets are tightened: in this way astronomers are often able to describe what types of planets cannot orbit a star.
M dwarfs such as Barnard's Star are more easily studied than larger stars in this regard because their lower masses render perturbations more obvious. Gatewood was thus able to show in 1995 that planets with 10 times the mass of Jupiter (the lower limit for brown dwarfs) were impossible around Barnard's Star, in a paper which helped refine the negative certainty regarding planetary objects in general. In 1999, work with the Hubble Space Telescope
further excluded planetary companions of 0.8 times the mass of Jupiter with an orbital period of less than 1,000 days (Jupiter's orbital period is 4,332 days), while Kuerster determined in 2003 that within the habitable zone
around Barnard's Star, planets are not possible with an "M sin i" value greater than 7.5 times the mass of the Earth, or with a mass greater than 3.1 times the mass of Neptune (much lower than van de Kamp's smallest suggested value).
While this research has greatly restricted the possible properties of planets around Barnard's Star, it has not ruled them out completely; terrestrial planets would be difficult to detect. NASA
's Space Interferometry Mission
, which was to begin searching for extrasolar Earth-like planets, had chosen Barnard's Star as a search target. However, this mission was shut down at the end of 2010, and is not expected to be funded again in the 2010s. (ESA's similar Darwin
interferometry mission had the same goal, but was stripped of funding in 2007 and is unlikely to be revived.)
. Undertaken between 1973 and 1978, it suggested that rapid, unmanned travel to another star system is possible with existing or near-future technology. Barnard's Star was chosen as a target, partly because it was believed to have planets.
The theoretical model suggested that a nuclear pulse rocket employing nuclear fusion
(specifically, electron bombardment of deuterium
and helium-3
) and accelerating for four years could achieve a velocity of 12% of the speed of light
. The star could then be reached in 50 years, within a human lifetime. Along with detailed investigation of the star and any companions, the interstellar medium
would be examined and baseline astrometric readings performed.
The initial Project Daedalus model sparked further theoretical research. In 1980, Robert Freitas
suggested a more ambitious plan: a self-replicating spacecraft intended to search for and make contact with extraterrestrial life
. Built and launched in Jovian
orbit, it would reach Barnard's Star in 47 years under parameters similar to those of the original Project Daedalus. Once at the star, it would begin automated self-replication, constructing a factory, initially to manufacture exploratory probes and eventually to create a copy of the original spacecraft after 1,000 years.
, suggested that the flare's temperature was 8000 K, more than twice the normal temperature of the star, although simply analyzing the spectra cannot precisely determine the flare's total output. Given the essentially random nature of flares, she noted "the star would be fantastic for amateurs to observe".
The flare was surprising because intense stellar activity is not expected around stars of such age. Flares are not completely understood, but are believed to be caused by strong magnetic fields which suppress plasma
convection
and lead to sudden outbursts: strong magnetic fields occur in rapidly rotating stars, while old stars tend to rotate slowly. An event of such magnitude around Barnard's Star is thus presumed to be a rarity. Research on the star's periodicity, or changes in stellar activity over a given timescale, also suggest it ought to be quiescent; 1998 research showed weak evidence for periodic variation in Barnard's Star's brightness, noting only one possible starspot over 130 days.
Stellar activity of this sort has created interest in using Barnard's Star as a proxy to understand similar stars. Photometric studies of its X-ray
and UV
emissions are hoped to shed light on the large population of old M dwarfs in the galaxy. Such research has astrobiological
implications: given that the habitable zones of M dwarfs are close to the star, any planets would be strongly influenced by solar flares, winds, and plasma ejection events.
, at 1.66 parsecs or 5.41 light years distance. The Sun and Alpha Centauri
are, respectively, the next closest systems. From Barnard's Star, the Sun would appear on the diametrically opposite side of the sky at coordinates RA=, Dec=, in the eastern part of the constellation Monoceros
. The absolute magnitude of the Sun is 4.83 and at a distance of 1.834 parsecs, it would be an impressively bright first-magnitude star, like Pollux
is from the Earth.
Red dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....
star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
approximately six light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s away from Earth in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
of Ophiuchus
Ophiuchus
Ophiuchus is a large constellation located around the celestial equator. Its name is from the Greek "serpent-bearer", and it is commonly represented as a man grasping the snake that is represented by the constellation Serpens. Ophiuchus was one of the 48 constellations listed by the 2nd-century...
(the Snake-holder). In 1916, the American astronomer
Astronomer
An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...
E.E. Barnard measured its proper motion
Proper motion
The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
as 10.3 arcsecond
Minute of arc
A minute of arc, arcminute, or minute of angle , is a unit of angular measurement equal to one sixtieth of one degree. In turn, a second of arc or arcsecond is one sixtieth of one minute of arc....
s per year, which remains the largest-known proper motion of any star relative to the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. At a distance of about 1.8 parsecs from the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
, or just under six light-years, Barnard's Star is the nearest known star in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Ophiuchus, and the fourth-closest known individual star to the Sun, after the three components of the Alpha Centauri
Alpha Centauri
Alpha Centauri is the brightest star in the southern constellation of Centaurus...
system. Despite its proximity, Barnard's Star, at a dim apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
of about nine, is not visible with the unaided eye; however, it is much brighter in infrared light than it is in visible light.
Barnard's Star has been the subject of much study, and it has probably received more attention from astronomers than any other class M dwarf star due to its proximity and favorable location for observation near the celestial equator
Celestial equator
The celestial equator is a great circle on the imaginary celestial sphere, in the same plane as the Earth's equator. In other words, it is a projection of the terrestrial equator out into space...
. Historically, research on Barnard's Star has focused on measuring its stellar characteristics, its astrometry
Astrometry
Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. The information obtained by astrometric measurements provides information on the kinematics and physical origin of our Solar System and our Galaxy, the Milky...
, and also refining the limits of possible extrasolar planet
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
s. Although Barnard's Star is an ancient star, some observations suggest that it still experiences star flare
Flare star
A flare star is a variable star that can undergo unpredictable dramatic increases in brightness for a few minutes. It is believed that the flares on flare stars are analogous to solar flares in that they are due to magnetic reconnection in the atmospheres of the stars. The brightness increase is...
events.
Barnard's Star has also been the subject of some controversy. For a decade, from the early 1960s to the early 1970s, Peter van de Kamp
Peter van de Kamp
Piet van de Kamp , known as Peter van de Kamp in the United States, was a Dutch astronomer who lived most of his life in the United States. He was professor of astronomy at Swarthmore College and director of the college's Sproul Observatory from 1937 until 1972...
claimed that there was a gas giant
Gas giant
A gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...
planet
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
(or planets) in orbit around it. While the presence of small terrestrial planets around the star remains a possibility, Van de Kamp's specific claims of large gas giant planets were refuted in the mid 1970s.
Barnard's Star is also notable as the target for Project Daedalus
Project Daedalus
Project Daedalus was a study conducted between 1973 and 1978 by the British Interplanetary Society to design a plausible unmanned interstellar spacecraft. Intended mainly as a scientific probe, the design criteria specified that the spacecraft had to use current or near-future technology and had to...
, a study on the possibility of fast, unmanned travel to nearby star systems
Interstellar travel
Interstellar space travel is manned or unmanned travel between stars. The concept of interstellar travel in starships is a staple of science fiction. Interstellar travel is much more difficult than interplanetary travel. Intergalactic travel, or travel between different galaxies, is even more...
.
Overview
Barnard's Star is a red dwarf of the dim spectral typeStellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
M4, and it is too faint to see without a telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
. Its apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
is 9.54. This compares with a magnitude of −1.5 for Sirius
Sirius
Sirius is the brightest star in the night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus, the next brightest star. The name "Sirius" is derived from the Ancient Greek: Seirios . The star has the Bayer designation Alpha Canis Majoris...
– the brightest star in the night sky – and about 6.0 for the faintest visible objects with the naked eye (this magnitude scale is logarithmic
Logarithmic scale
A logarithmic scale is a scale of measurement using the logarithm of a physical quantity instead of the quantity itself.A simple example is a chart whose vertical axis increments are labeled 1, 10, 100, 1000, instead of 1, 2, 3, 4...
, and so the magnitude of 9.54 is only about 1/27th of the brightness of the faintest star that can be seen with the naked eye under good viewing conditions).
At seven to 12 billion years of age, Barnard's Star is considerably older than the Sun, and it might be among the oldest stars in the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
galaxy. Barnard's Star has lost a great deal of rotational energy, and the periodic slight changes in its brightness indicate that it rotates just once every 130 days (compared with just over 25 days for the Sun). Given its age, Barnard's Star was long assumed to be quiescent in terms of stellar activity. However in 1998, astronomers observed an intense stellar flare, surprisingly showing that Barnard's Star is a flare star
Flare star
A flare star is a variable star that can undergo unpredictable dramatic increases in brightness for a few minutes. It is believed that the flares on flare stars are analogous to solar flares in that they are due to magnetic reconnection in the atmospheres of the stars. The brightness increase is...
. Barnard's Star has the variable star
Variable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
designation
Variable star designation
Variable stars are named using a variation on the Bayer designation format of an identifying label combined with the Latin genitive of the name of the constellation in which the star lies...
V2500 Ophiuchi. In 2003, Barnard's Star presented the first detectable change in the radial velocity
Radial velocity
Radial velocity is the velocity of an object in the direction of the line of sight . In astronomy, radial velocity most commonly refers to the spectroscopic 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.
The radial velocity of Barnard's Star towards the Sun can be measured by its blue shift
Blue shift
A blueshift is any decrease in wavelength ; the opposite effect is referred to as redshift. In visible light, this shifts the colour from the red end of the spectrum to the blue end...
. Two measurements are given in catalogue
Star catalogue
A star catalogue, or star catalog, is an astronomical catalogue that lists stars. In astronomy, many stars are referred to simply by catalogue numbers. There are a great many different star catalogues which have been produced for different purposes over the years, and this article covers only some...
s: 106.8 km/s in SIMBAD
SIMBAD
SIMBAD is an astronomical database of objects beyond the Solar System...
, which refers to a 1967 compilation of older measurements, and 110.8 km/s in ARICNS and similar values in all modern astronomical references. These measurements, combined with proper motion, suggest a true velocity relative to the Sun of 139.7 and 142.7 km/s, respectively. Barnard's Star will make its closest approach to the Sun around AD 11,700, when it approaches to within about 3.8 light-years. However, at that time, Barnard's Star will not be the nearest star, since Proxima Centauri
Proxima Centauri
Proxima Centauri is a red dwarf star about 4.2 light-years distant in the constellation of Centaurus. It was discovered in 1915 by Robert Innes, the Director of the Union Observatory in South Africa, and is the nearest known star to the Sun, although it is too faint to be seen with the naked eye...
will have moved even closer to the Sun. Barnard's Star will still be too dim to be seen with the naked eye at the time of its closest approach, since its apparent magnitude will be about 8.5 then. After that it will gradually recede from the Sun.
Barnard's Star has approximately 17% of a solar mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
, and it has a radius 15% to 20% of that of the Sun. In 2003, its radius was estimated as 0.20±0.008 of the solar radius, at the high end of the ranges that were typically calculated in the past, indicating that previous estimates of the radius of Barnard's Star probably underestimated the actual value. Thus, although Barnard's Star has roughly 180 times the mass of Jupiter, its radius is only 1.5 to 2.0 times larger, reflecting the tendency of objects in the brown dwarf
Brown dwarf
Brown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth...
range to be about the same size. Its effective temperature
Effective temperature
The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation...
is 3,134(±102) kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
, and it has a visual luminosity just 4/10,000ths of solar luminosity, corresponding to a bolometric luminosity of 34.6/10,000ths. 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 Unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
s.
In a broad survey of the metallicity
Metallicity
In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium...
of M-class dwarf stars, Barnard's Star's was placed between −0.5 and −1.0 on the metallicity scale, which is roughly 10 to 32% of the value for the Sun. Metallicity, the proportion of stellar mass made up of elements heavier than helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
, 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 star
Halo Star
Halo Star is the ninth studio album by the Darkwave band Black Tape for a Blue Girl. It was released in 2004 by Projekt Records. It includes one of the band's most popular songs, "Knock Three Times," which later appeared on the popular 2005 Projekt Presents: A Dark Cabaret compilation, remixed as...
s. While sub-solar, Barnard's Star's metallicity is higher than 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.
Claims of a planetary system
For a decade from 1963 to about 1973, a substantial number of astronomers accepted a claim by Peter van de KampPeter van de Kamp
Piet van de Kamp , known as Peter van de Kamp in the United States, was a Dutch astronomer who lived most of his life in the United States. He was professor of astronomy at Swarthmore College and director of the college's Sproul Observatory from 1937 until 1972...
that he had detected, by using astrometry, a perturbation in the proper motion
Proper motion
The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
of Barnard's Star consistent with its having one or more planets comparable in mass with Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
. Van de Kamp had been observing the star from 1938, attempting, with colleagues at the Swarthmore College
Swarthmore College
Swarthmore College is a private, independent, liberal arts college in the United States with an enrollment of about 1,500 students. The college is located in the borough of Swarthmore, Pennsylvania, 11 miles southwest of Philadelphia....
observatory, to find minuscule variations of one micrometre
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
in its position on photographic plates consistent with orbital perturbations (wobbles) in the star that would indicate a planetary companion; this involved as many as ten people averaging their results in looking at plates, to avoid systemic, individual errors. Van de Kamp's initial suggestion was a planet having about 1.6 the Jovian mass at a distance of 4.4 AU in a slightly eccentric orbit, and these measurements were apparently refined in a 1969 paper. Later that year, Van de Kamp suggested that there were two planets of 1.1 and 0.8 Jovian masses.
Van de Kamp never acknowledged any error and published a further confirmation of two planets' existence as late as 1982; he died in 1995. Wulff Heintz, Van de Kamp's successor at Swarthmore and an expert on double stars, questioned his findings and began publishing criticisms from 1976 onwards. The two men were reported to have become estranged from each other because of this.
Refining planetary boundaries
While not completely ruling out the possibility of planets, null results for planetary companions continued throughout the 1980s and 1990s, the latest based on interferometric work with the Hubble Space TelescopeHubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
in 1999. By refining the values of a star's motion, the mass and orbital boundaries for possible planets are tightened: in this way astronomers are often able to describe what types of planets cannot orbit a star.
M dwarfs such as Barnard's Star are more easily studied than larger stars in this regard because their lower masses render perturbations more obvious. Gatewood was thus able to show in 1995 that planets with 10 times the mass of Jupiter (the lower limit for brown dwarfs) were impossible around Barnard's Star, in a paper which helped refine the negative certainty regarding planetary objects in general. In 1999, work with the Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
further excluded planetary companions of 0.8 times the mass of Jupiter with an orbital period of less than 1,000 days (Jupiter's orbital period is 4,332 days), while Kuerster determined in 2003 that within the habitable zone
Habitable zone
In astronomy and astrobiology, a habitable zone is an umbrella term for regions that are considered favourable to life. The concept is inferred from the empirical study of conditions favourable for Life on Earth...
around Barnard's Star, planets are not possible with an "M sin i" value greater than 7.5 times the mass of the Earth, or with a mass greater than 3.1 times the mass of Neptune (much lower than van de Kamp's smallest suggested value).
While this research has greatly restricted the possible properties of planets around Barnard's Star, it has not ruled them out completely; terrestrial planets would be difficult to detect. NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
's Space Interferometry Mission
Space Interferometry Mission
The Space Interferometry Mission, or SIM, also known as SIM Lite , was a planned space telescope developed by the U.S. National Aeronautics and Space Administration , in conjunction with contractor Northrop Grumman...
, which was to begin searching for extrasolar Earth-like planets, had chosen Barnard's Star as a search target. However, this mission was shut down at the end of 2010, and is not expected to be funded again in the 2010s. (ESA's similar Darwin
Darwin (ESA)
Darwin was a suggested ESA Cornerstone mission which would have involved a constellation of four to nine spacecraft designed to directly detect Earth-like planets orbiting nearby stars and search for evidence of life on these planets...
interferometry mission had the same goal, but was stripped of funding in 2007 and is unlikely to be revived.)
Project Daedalus
Excepting the planet controversy, the best known study of Barnard's Star was part of Project DaedalusProject Daedalus
Project Daedalus was a study conducted between 1973 and 1978 by the British Interplanetary Society to design a plausible unmanned interstellar spacecraft. Intended mainly as a scientific probe, the design criteria specified that the spacecraft had to use current or near-future technology and had to...
. Undertaken between 1973 and 1978, it suggested that rapid, unmanned travel to another star system is possible with existing or near-future technology. Barnard's Star was chosen as a target, partly because it was believed to have planets.
The theoretical model suggested that a nuclear pulse rocket employing nuclear fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
(specifically, electron bombardment of deuterium
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...
and helium-3
Helium-3
Helium-3 is a light, non-radioactive isotope of helium with two protons and one neutron. It is rare on Earth, and is sought for use in nuclear fusion research...
) and accelerating for four years could achieve a velocity of 12% of the speed of light
Speed of light
The speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...
. The star could then be reached in 50 years, within a human lifetime. Along with detailed investigation of the star and any companions, the interstellar medium
Interstellar medium
In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...
would be examined and baseline astrometric readings performed.
The initial Project Daedalus model sparked further theoretical research. In 1980, Robert Freitas
Robert Freitas
Robert A. Freitas Jr. is a Senior Research Fellow, one of four researchers at the nonprofit foundation Institute for Molecular Manufacturing in Palo Alto, California. He holds a 1974 Bachelor's degree majoring in both physics and psychology from Harvey Mudd College, and a 1978 Juris Doctor degree...
suggested a more ambitious plan: a self-replicating spacecraft intended to search for and make contact with extraterrestrial life
Extraterrestrial life
Extraterrestrial life is defined as life that does not originate from Earth...
. Built and launched in Jovian
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
orbit, it would reach Barnard's Star in 47 years under parameters similar to those of the original Project Daedalus. Once at the star, it would begin automated self-replication, constructing a factory, initially to manufacture exploratory probes and eventually to create a copy of the original spacecraft after 1,000 years.
The flare in 1998
The observation of a stellar flare on Barnard's Star has added another element of interest to its study. Noted by William Cochran, University of Texas at Austin, based on changes in the spectral emissions on July 17, 1998 (during an unrelated search for planetary "wobbles"), it was four more years before the flare was fully analyzed. At that point Diane Paulson et al., now of Goddard Space Flight CenterGoddard Space Flight Center
The Goddard Space Flight Center is a major NASA space research laboratory established on May 1, 1959 as NASA's first space flight center. GSFC employs approximately 10,000 civil servants and contractors, and is located approximately northeast of Washington, D.C. in Greenbelt, Maryland, USA. GSFC,...
, suggested that the flare's temperature was 8000 K, more than twice the normal temperature of the star, although simply analyzing the spectra cannot precisely determine the flare's total output. Given the essentially random nature of flares, she noted "the star would be fantastic for amateurs to observe".
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
and lead to sudden outbursts: strong magnetic fields occur in rapidly rotating stars, while old stars tend to rotate slowly. An event of such magnitude around Barnard's Star is thus presumed to be a rarity. Research on the star's periodicity, or changes in stellar activity over a given timescale, also suggest it ought to be quiescent; 1998 research showed weak evidence for periodic variation in Barnard's Star's brightness, noting only one possible starspot over 130 days.
Stellar activity of this sort has created interest in using Barnard's Star as a proxy to understand similar stars. Photometric studies of its X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
and UV
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
emissions are hoped to shed light on the large population of old M dwarfs in the galaxy. Such research has astrobiological
Astrobiology
Astrobiology is the study of the origin, evolution, distribution, and future of life in the universe. This interdisciplinary field encompasses the search for habitable environments in our Solar System and habitable planets outside our Solar System, the search for evidence of prebiotic chemistry,...
implications: given that the habitable zones of M dwarfs are close to the star, any planets would be strongly influenced by solar flares, winds, and plasma ejection events.
The star's neighborhood
Barnard's Star shares much the same neighborhood as the Sun. The neighbors of Barnard's Star are generally of red dwarf size, the smallest and most common star type. Its closest neighbor is currently the red dwarf Ross 154Ross 154
Ross 154 is a red dwarf star approximately 3.0 pc or 9.68 light years from the Sun. It is the nearest star in the southern constellation Sagittarius, and one of the closest to the Sun...
, at 1.66 parsecs or 5.41 light years distance. The Sun and Alpha Centauri
Alpha Centauri
Alpha Centauri is the brightest star in the southern constellation of Centaurus...
are, respectively, the next closest systems. From Barnard's Star, the Sun would appear on the diametrically opposite side of the sky at coordinates RA=, Dec=, in the eastern part of the constellation Monoceros
Monoceros
Monoceros is a faint constellation on the celestial equator. Its name is Greek for unicorn. Its definition is attributed to the 17th-century Dutch cartographer Petrus Plancius. It is bordered by Orion to the west, Gemini to the north, Canis Major to the south and Hydra to the east...
. The absolute magnitude of the Sun is 4.83 and at a distance of 1.834 parsecs, it would be an impressively bright first-magnitude star, like Pollux
Pollux (star)
Pollux is an orange giant star approximately 34 light-years from the Earth in the constellation of Gemini . Pollux is the brightest star in the constellation, brighter than Castor...
is from the Earth.
See also
- List of nearest stars
- Stars and planetary systems in fiction#Barnard's Star
- Stars named after peopleStars named after peopleOver the past few centuries, a small number of stars have been named after individual people. It is common in astronomy for objects to be given names, in accordance with accepted astronomical naming conventions...