Vega

System Summary

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.

Royal Observatory, Edinburgh





Larger illustration.





Vega is the brightest star
in Constellation Lyra, the
Lyre or Harp.

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).

NASA Observatorium




See a discussion of
the "main sequence"
as part of stellar
evolution and death.

The Star

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).

Jason P. Aufdenberg,
NOAO, AURA, NSF




Larger image.




Vega rotates so
fast that it is
cooler as well
as wider at its
equator than at
its poles (more).

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.

Two Dust Disks?

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 (Harvey 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 (van 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 Holweger 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)

Closest Neighbors

The following star systems are located within 10 light-years of Vega.

Other Information

• Try Professor Jim Kaler's Stars site for other information about Vega at the University of Illinois' Department of Astronomy.

• 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.