Vega






Vega is the brightest star in Lyra, and the fifth brightest star in the sky. It is the third brightest star in the Northern night sky, after Sirius and Arcturus, and can often be seen near the zenith in the mid-northern latitudes during the Northern Hemisphere summer.

It is a "nearby star" from Earth, and together with Arcturus and Sirius, one of the brightest stars in the Sun's neighbourhood.Vega is a vertex of the Summer Triangle, which consists of Vega (in Lyra), Deneb (in Cygnus) and Altair (in Aquila). If one is to consider this asterism a right triangle, then Vega would correspond to its right angle.

This triangle is very recognizable in the northern skies for there are few bright stars in its vicinity.

Its spectral class is A0 V (Sirius, an A1 V, is slightly less luminous) and it is firmly in the main sequence (dwarf), fusing hydrogen to helium in its core. It is twice as massive as our Sun and about fifty times as luminous.

Vega's current age is about 500 million years. Since more powerful stars use their fusion fuel more quickly than smaller ones, Vega's estimated lifetime is only one billion years, approximately a tenth that of our Sun.

After it leaves the main sequence, Vega is likely to become a yellow giant similar to Capella and Eta2 Hydri before entering the red giant stage, after which it will eventually shed its outer layers to become a white dwarf.

In about 14,000 AD, Vega will become the North Star, owing to the precession of the equinoxes. See Polaris for more information.

Professional astronomers have used Vega for the calibration of absolute photometric brightness scales. When the magnitude scale was fixed, Vega happened to be close to zero magnitude.

Therefore the visual magnitude of Vega was decided to be, by definition, zero at all wavelengths for many years (this is no longer the case, as the apparent magnitude zero point is now most commonly defined in terms of a particular numerically specified flux).

It also has a relatively flat electromagnetic spectrum in the visual region (wavelength range 350-850 nanometers, most of which can be seen with the human eye), so the flux densities are roughly equal, 2000-4000 Jy. The flux density of Vega drops rapidly in the infrared, and is near 100 Jy at 5 micrometres.

We see Vega from within 5 degrees of the polar (rotation) axis, but if you were looking along the plane of the equator, Vega would look about 23% fatter at the equator because Vega rotates at 93% of the speed that would cause it to start breaking up from centrifugal effects , which has to be taken into account when investigating properties of the star's dust disk and environment.

The name Vega comes from the Arabic word waqi meaning "falling", via the phrase "the swooping vulture". As part of the constellation Lyra it represents a jewel set in the body of the harp.




Possible Solar System

Dust disk

In 1983, an orbiting satellite called IRAS discovered far more infrared radiation coming from Vega than expected for small interstellar dust grains found around young, early-type stars. 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. The disk is thought to be made of icy dust particles that have been warmed by the star which tends to develop after most of the surrounding nebulae of gas has been absorbed or expelled from the developing star.

In 1998, British and American astronomers obtained the first pictures of a huge disk-like structure of dust enshrouding Vega in a roughly circular envelope. The "sub-millimeter" image shows emissions from tiny dust particles 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 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. The disk appears to be mostly composed of fine dust particles that are probably created by the collision of protoplanetary bodies within approximately 90 AUs of the star but are then blown away by its intense radiation. On the other hand, the mass and short lifetime 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).

On April 11, 2006, an international team of astronomers announced the detection of a weak near-infrared flux in the vicinity of Vega (78 times less important than that of the star) thanks the CHARA array located at Mount Wilson, CA[2]. This flux is thought to come from dust particles located at only a fraction of an astronomical unit from Vega (much closer than the dust previously detected around Vega and other Vega-type stars) and heated by the star to temperatures close to 1300 íC.

The dust grains are suspected to be on average smaller that in our Solar system, with typical diameters below one micrometre (equivalent to particles constituting cigarette smoke). Such small grains should normally be rapidly blown out by the radiation pressure created by the intense stellar flux. Their abundance thus proves that they are produced in permanence, probably in a phase of intense meteoritic and cometary bombardment like those experienced by the Earth at the origins of the solar system. The dust production rate would correspond in the daily passing of 13 large comets in the environment of Vega.




Possible Planetary System

In 2000, a team of astronomers announced that modeling 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.

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.

The two teams, led by David Koerner using the Owens Valley Radio Observatory, 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.

Modeling simulations by Wilner's team suggested that the semimajor axis of the planet's orbit may center around 30 AUs. 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, according to Marc Kuchner, the team's theorist.

Other simulations 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.

In 2003, astronomers 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 roughly similar to those held by the same planets in the Solar System.

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. This same process is thought to have happened in the Solar System as well under a new theory.




Cultural Significance

The star, Vega, has been the subject of many 'firsts' in Astronomy; in 1850 it became the first star to be photographed, and in 1872 the first to have its spectrum photographed. It was also debatably the first star to have its parallax measured, in the pioneering experiments of Friedrich Struve in 1837. Finally, it became the first star to have a car named after it, when Chevrolet launched the 'Vega' in 1971.




Alternative and Former Names

Babylonia: Dilgan - 'The Messenger of Light'

Akkadia: Tir-anna - 'Life of Heaven'

Greece: Allore, Alahore, and Alohore

Arabic: Wega

China: Zhi-Nu - 'The Weaver' - and her beloved shepherd, Altair, who meet once a year, crossing the Milky Way.

Hindu: Sanskrit: Abhijit "Victorious"

Latin: Fidis, "Lyre"; Vultur cadens, "Falling vulture"

Medieval astrologers counted Vega as one of the Behenian stars and related it to chrysolite and winter savory. Cornelius Agrippa listed its kabbalistic sign under Vultur cadens, a literal Latin translation of the Arabic name.

Vega was one of the stars in the Hindu 20th nakshatra, Abhtlit, "Victorious", the most northern of these stellar divisions and far out of the moon's path [usually the stars in moon mansions are ecliptic stars], but apparently utilized to bring in this splendid object; or, as Mueller says, because it was of specially good omen, for under its influence the gods had vanquished the Asuras; these last being the Hindu divinities of evil, similar to the Titans of Greece.

Ancient Hindus saw it as a triangle, or as the three-cornered nut of the aquatic plant Cringata. Vega, along with Deneb Adige in the Swan, and Altair in the Eagle, forms the Great Summer Triangle. The summer triangle consists of Deneb - Altair - and Vega.




In the News ...


Massive Asteroid Belts Discovered Around Vega   Discovery - January 9, 2013

Vega is famous for being the fifth-brightest star in global skies, but it may soon also become famous for sporting two asteroid belts and, by extension, an entire system of exoplanets. The young Vega system is, by its nature, thick with dust and debris from the recent frenzy of star formation. The solar system on the other hand is much older and has had time to "settle"; dust has coalesced to form larger chunks of debris (asteroids, comets, planets). But the gap between the two asteroid belts is possibly the most fascinating discovery -- that could be a zone where young planets roam. Findings echo recent results showing multiple-planet systems are common beyond our sun. Spitzer and Herchel were able to see the two belts of rocky debris from the dust they produce -- asteroids bump, grind and collide, kicking up dust. The radiation from the star then heated the dust, which, in turn, glows in infrared light.


Magnetic field on bright star Vega   PhysOrg - June 23, 2009
Vega is a famous star among amateur and professional astronomers. Located at only 25 light years from Earth in the Lyra constellation, it is the fifth brightest star in the sky. It has been used as a reference star for brightness comparisons. Vega is twice as massive as the Sun and has only one tenth its age. Because it is both bright and nearby, Vega has been often studied but it is still revealing new aspects when it is observed with more powerful instruments. Vega rotates in less than a day, while the Sun's rotation period is 27 days. The intense centrifugal force induced by this rapid rotation flattens its poles and generates temperature variations of more than 1000 degrees Celsius between the polar (warmer) and the equatorial regions of its surface. Vega is also surrounded by a disk of dust, in which the inhomogeneities suggest the presence of planets.


Dusty Aftermath Of Pluto-Sized Collision Science Daily - January 2005

NASA's Spitzer Space Telescope has seen the dusty aftermath of this "run-in." Astronomers think embryonic planets smashed together, shattered into pieces and repeatedly crashed into other fragments to create ever-finer debris. Vega's light heats the debris, and Spitzer's infrared telescope detects the radiation. Vega, located 25 light-years away in the constellation Lyra, is the fifth brightest star in the night sky. It is 60 times brighter than our Sun. Observations of Vega in 1984, with the Infrared Astronomical Satellite, provided the first evidence for dust particles around a typical star. Because of Vega's proximity and because its pole faces Earth, it provides a great opportunity for detailed study of the dust cloud around it.



LYRA




ASTRONOMY INDEX


ALPHABETICAL INDEX OF ALL FILES


CRYSTALINKS MAIN PAGE


PSYCHIC READING WITH ELLIE


2012 THE ALCHEMY OF TIME