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Also known as Alpha Lyrae, Vega is located within 25.3 light-years (ly) away from our Sun, Sol, as the brightest star in Constellation Lyra, the Lyre or Harp. Its name (more correctly "Wega") is derived from the Arabic for "Swooping Eagle" ("Al Nasr al Waki"). The star is the lower right member (18:36:56.34+38:47:01.29, ICRS 2000.0) of the "Summer Triangle" of first magnitude stars viewed from the northern hemisphere, formed with Altair (Alpha Aquilae) at the lower left, and Deneb (Alpha Cygni) at upper right. This zero-magnitude star is visible with the naked eye as the third brightest star after Sirius A and Arcturus in Earth's northern skies, and is fifth brightest star overall. Due to the slowly changing orientation of Earth's axis in space (which is also known as the Precession of the Equinoxes), Vega was the North Celestial Pole Star some 12,000 years ago and will be again in another 10,000 years.
Vega was the first star to be photographed, exposed for 100 seconds with the daguerreotype process through a 15-inch refractor at Harvard Observatory on the night of July 16-17, 1850. Two nearby stars have been determined in subsequent observations to be optical companions only. In late 2003, astronomers announced that the latest computer models indicate that the structure of a faint dust disk observed around Vega can be best explained by the presence of Neptune-sized and Jupiter-sized planets orbiting at distances roughly similar to those held by their apparent "cousins" in the Solar System (more discussion below -- ROE press release). On January 10, 2005, astronomers using the infrared Spitzer Space Telescope announced that the dust disk is bigger than previously estimated and was probably created by collisions of protoplanetary objects as big as the planet Pluto, up to 2,000 kilometers (about 1,200 miles) in diameter (press release -- more below). On January 10, 2006, astronomers using the infrared Center for High Angular Resolution Astronomy (CHARA) Array announced their finding that Vega rotates so fast that it is cooler as well as 23 percent wider along its equator than at its poles due to the gravitational effect of its "middle bulge" (NOAO press release; AAS 207 session summary; and Aufdenberg et al, 2006 -- more below).
Vega is a slightly bluish, white main sequence dwarf star of spectral and luminosity type A0 V, like Sirius. Although the star was estimated previously to have 2.3 to 3.1 times Sol's mass, a 2012 analysis now suggests around 2.15 Solar-masses (Ken Croswell, Science Now, December 3, 2012 and Monnier et al, 2012). Vega may also have 2.73 +/- 0.01 times its diameter (Aufdenberg et al, 2006; and Ciardi et al, 2001) and 37 +/- 3 times (true A0V average derived by Aufdenberg et al, 2006) to 58 times (pole on) its luminosity. Like Sirius, however, Vega radiates much more in ultraviolet wavelengths than Sol, and, not surprisingly, the European Space Agency has used ultraviolet spectral flux distribution data to determine stellar effective temperatures and surface gravities, including those of Vega. The star may be about only 63 percent as enriched as Sol with elements heavier than hydrogen ("metallicity") based on its abundance of iron (D. Gigas, 1986, but more recent findings on Vega's mild underabundance of metals can be found in Ilijic et al, 1998). On the other hand, its iron metallicity has been measured anywhere from four to 115 percent of Sol's (Cayrel de Strobel et al, 1991, page 31).
Previously estimated to be only around 200 to 350 million years old (Maeder and Meynet, 1988), more recent estimates of its mass indicate an age of around 625 to 850 million years (Ken Croswell, Science Now, December 3, 2012 and Monnier et al, 2012). As Vega is so much bigger and hotter than Sol, however, the star will exhaust its core hydrogen after only another 650 million years or so (for a total life of around a billion years) and turn into a red giant or Cepheid variable before puffing away its outer layers to reveal a remnant core as a white dwarf. The star is a rapidly rotating star whose apparent "pole-on" view from Earth distorts its various stellar characteristics (Aufdenberg et al, 2006; and Gulliver et al, 1994).
On January 10, 2006, astronomers using the infrared Center for High Angular Resolution Astronomy (CHARA) Array announced that Vega rotates so fast (at around 91 percent of its "break-up rate") that it is cooler as well as 23 percent wider along its equator than at its poles due to the gravitational effect of its "middle bulge" (NOAO press release; AAS 207 session summary); and Aufdenberg et al, 2006). Although our Sun, Sol, takes around 25.4 days to complete its rotation at its equator, Vega takes only 12.5 hours. Models of Vega based on CHARA observations suggest that the star is rotating at about 91 +/- 3 percent of the speed (angular velocity) that would cause it to physically fly apart. Moreover, strong darkening observed around Vega's equator indicates that the star's surface at the equator is around 4,000 degrees Fahrenheit (2,300° Kelvin) cooler than at its poles. This effect, known as “gravity darkening,” was first predicted in 1924 by theoretical astronomer Edvard Hugo von Zeipel (1873-1959). The observations are consistent with the hypothesis that Vega is viewed with its pole of rotation pointing toward Earth (first proposed by astronomer Richard O. Gray), so that the relatively cool equator corresponds to the darker "limb of the star" and heightens the gravity-darkening effect.
Vega is a Delta Scuti type of pulsating variable star (over 0.1903 days) whose slight variations have been a matter of debate since their detection in 1918 by Paul Guthnick (1879-1947) and Richard Prager (1883-1945) (Vasil'yev et al, 1989). It has been given the New Suspected Variable designation NSV 11128. Useful star catalogue numbers for Vega include: Alp or Alf Lyr, 3 Lyr, HR 7001, Gl 721, Hip 91262, HD 172167, BD+38 3238, SAO 67174, FK5 699, LTT 15486, LTT 15486, and ADS 11510 A.
In 1983, an orbiting satellite called IRAS discovered far more infrared
radiation -- which has waves longer than red light -- coming from the
Vega than expected for small interstellar dust grains found around
young, early-type stars
et al, 1984). The radiation is coming from a huge circular shell
of dust surrounds the star extending outwards to 140 AU in radius, much
like those that encompass Fomalhaut, Beta Pictoris, and Denebola
der Bliek et al, 1994). The disk is thought to be made of icy dust particles that
have been warmed by the star which, according to
et al (1999), tends to develop after most of the surrounding
nebulae of gas has been absorbed or expelled from the developing star.
Submillimetre Common-User Bolometer Array, James Clerk Maxwell Telescope, JAC
(Cold dust disk around Vega)
In 1998, British and American astronomers at the Joint Astronomy Center (JAC press release) in Hawaii, the University of California in Los Angeles (UCLA), and the Royal Observatory of Edinburgh obtained the first pictures of a huge disk-like structure of dust enshrouding Vega in a roughly circular envelope (Holland et al, 1998, in postscript). The "sub-millimeter" image, above, shows emissions from tiny dust particles (that are only a fraction of a millimeter in size) in orbit around Vega. Yellow to red areas of the image indicate the highest concentrations of cold dust, while blue to black areas suggest very little dust. In JAC's image the brightest emission area which indicates the greatest concentration of dust, is centered not on Vega but on a spot located from the star about twice the distance between Pluto and the Sun in the Solar system. A search with the Keck Telescope (located also on Mauna Kea in Hawaii) by the JAC astronomers failed to reveal infrared light from possible planets or brown dwarfs. If the blob of dust is associated with Vega, it could be a dust cloud around a giant planet orbiting Vega.
On January 10, 2005, astronomers using the infrared Spitzer Space Telescope announced that the dust disk is bigger than previously estimated (press release). The disk appears to be mostly composed of fine dust particles that are probably created by from collisions of protoplanetary bodies with around 90 AUs of the star but are then blown away by its intense radiation. On the other hand, the mass and short lifetime (dissipating with a 1,000 years) of these small particles indicate that the disk detected was created by a large and relatively recent collision that may have involved objects as big as the planet Pluto (up to 2,000 kilometers or around 1,200 miles in diameter).
A Planetary System?
In 2000, a team of astronomers (Nick N. Gorkavyi, Sara Heap, Leonid Ozernoy, Tanya A. Taidakova, and John Mather) announced that modelling of the asymmetric circumstellar disk infalling into Vega suggests that there may be a planet twice the mass of Jupiter at an orbital distance of about 50 to 60 AU from the star -- up to one and a half times the "average" orbital distance of Pluto in the Solar System (N.N. Gorkavyi et al, 2000 and more discussion).
At the January 2002, 199th Meeting of the American Astronomical Society in Washington, DC, two teams of astronomers announced that the cold dust in Vega's circumstellar disk is at least partly gathered into large clumps, in a characteristic shape that suggests the gravitational influence of a giant planet in an eccentric orbit (Abstracts for sessions 66.04 and 66.05, and CfA press release). The two teams, led by David Koerner (of the Planetary Origins Research Group at the University of Pennsylvania) using the Owens Valley Radio Observatory and David Wilner (of the Harvard-Smithsonian Center for Astrophysics) using the Plateau de Bure Interferometer of the Institut de RadioAstronomie Millimetrique (IRAM) in the French Alps, collected millimeter-wavelength observations that were sensitive to structures as small as 20 AUs. They managed to resolve two knots in the circumstellar dust that were offset at 60 and 75 AUs from Vega. The dust would tend to become trapped in the hypothesized planet's mean-motion resonances around Vega. Detailed study of features in its dust cloud is possible because Vega is viewed nearly pole-on from Earth.
to Saturn and Titan
Many computer simulations of the
structure of the dust disk and its
clumps suggested that a Jupiter-like
gas giant had cleared out the inner
part of Vega's dust dusk.
Modelling simulations by Wilner's team (including Matt Holman, Paul Ho, and Marc Kuchner) suggested that the semimajor axis of the planet's orbit may center around 30 AUs -- at Neptune's orbital distance in the Solar System. The simulations also indicated that the planet must be smaller than 30 times Jupiter's mass. A larger planetary mass would cause the observed dust clumps to overlap by destroying and the hypothesized orbital resonances. (See Marc Kuchner's animation of the dust cloud and a hypothesized Jupiter-class planet around Vega.)
Other simulations by Nick N. Gorkavyi and Tanya A. Taidakova (Schafer Corporation) of an observed dust disk ring arc at 95 AUs also suggested that there may be a sub-Jovian planet between 90 to 100 AUs out from Vega. The simulations indicated that one (or more) very massive planet within 50 to 60 AUs may have destroyed the inner circumstellar dust disk by gravitational scattering (Abstract for 2002 AAS session 86.07).
In 2003, astronomers at the UK Astronomy Technology Centre at the Royal Observatory, Edinburgh announced that "new computer modelling techniques" show that observations of the structure of the faint dust disk around Vega can be best explained by the presence of Neptune-sized and Jupiter-sized planets orbiting at distances rouhgly similar to those held by the same planets in the Solar System (press release). The modelling suggested that a Neptune-like planet actually formed much closer to Vega and was pushed by a Jupiter-like planet in an inner orbit out to its current wide orbit around 80 AUs away from Vega over about 56 million years, sweeping many comets out with it and causing the dust disk to become clumpy (Mark C. Wyatt, 2003). This same process is thought to have happened in the Solar System as well under a new theory (space.com article; Levison, Morbidelli, and Gomes, Icarus, 2004; Robert Gomes, Nature, November 27, 2003; and Thommes et al, 2003).
Hunt for Earth-like Planets
The distance from Vega where an Earth-type planet would be "comfortable" with liquid water is centered around 7.1 AU -- between the orbital distances of Jupiter and Saturn in the Solar System. At that distance from the star, such a planet would have an orbital period close to 10.9 Earth years. If there is life on any Earth-type planet orbiting youthful Vega, it is likely to be primitive single-cell, anaerobic (non-oxygen producing) bacteria under constant bombardment by meteorites and comets as Earth was for the first billion years. Since there is unlikely to be free oxygen in the atmosphere of such a planet, it probably would not have an ozone layer (O3) although Vega puts out a lot more hard radiation (especially ultraviolet) than Sol.
The following star systems are located within 10 light-years of Vega.
|Star System||Spectra &|
|G 184-19 AB||M4.5 V |
|Mu Herculis4?||G5 IV |
|G 203-47||M3.5 V||7.4|
|BD+43 2796||M3.5 V||7.8|
|BD+45 2505 AB||M3 V |
|AC+20 1463-148 A||M2 V-VI||9.3|
|AC+20 1463-148 B||M2 V-VI||9.7|
Up-to-date technical summaries on these stars can be found at: the Astronomiches Rechen-Institut at Heidelberg's ARICNS, the Nearby Stars Database, and the Research Consortium on Nearby Stars (RECONS) list of the 100 Nearest Star Systems. Additional information may be available at Roger Wilcox's Internet Stellar Database.
Although Constellation Lyra (the Lyre) is thought to represent the harp given by Apollo to Orpheus, it represented the Vulture for the Ancient Egyptians and Greeks, who regarded the Vulture as one of three birds hunted by Hercules -- together with Cygnus (the Swan and Aquila (the Eagle). In another myth, however, Mercury was said to have invented the lyre by placing strings across the back of a tortoise shell, and so sometimes this constellation was drawn as a tortoise. For more information about the stars and objects in this constellation, go to Christine Kronberg's Lyra. For an illustration, see David Haworth's Lyra.
For more information about stars including spectral and luminosity class codes, go to ChView's webpage on The Stars of the Milky Way.
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