Vega (Alpha Lyrae)
The brightest star in the constellation Lyra,
the brightest star in the northern summer sky (forming the northwestern
apex of the Summer Triangle), and the fifth brightest star in the whole
sky. Its name derives from an Arabic phrase that means "the swooping eagle."
Vega is a main sequence A star that has the
distinction of being the first star ever to be captured on a photographic
plate (1850). At one time, Vega was the pole
star and will be so again in about 11,500 years.
| Vega. Image: Spitzer Space Telescope
disk around Vega
In 1983, based on observations by the Infrared
Astronomy Satellite (IRAS), Vega became one of the first stars to be
discovered with a large luminous infrared-radiating halo that suggests a
circumstellar cloud of warm dust. Since Vega seems to be rotating with its
pole directed toward Earth, the dust cloud probably represents a face-on
disk that may not be unlike the disk surrounding the Sun and that contains
the planets. Observations carried out by Helen Walker of the Rutherford
Appleton Laboratory, England, and associates, using the Infrared
Space Observatory, have shown that the Vegan disk contains particles
200 microns across, or 200 times larger than a typical interstellar dust
Planets around Vega?
In 2002, astronomers announced that two prominent peaks of dust emission
around Vega, one offset 60 AU to the southwest of the star, and the other
offset 75 AU to the northeast, could be best explained by the dynamical
influence of an unseen planet in an eccentric orbit. A massive planet in
an eccentric orbit within an in-spiraling dust cloud doesn't create a simple
ring like the Earth. Instead, calculations show that an eccentric planet
traps dust in two main concentrations at different distances from the star,
at positions outside the planet orbit that are generally not in line with
the star. Computer simulations show that this effect appears over a wide
range of planet masses and orbital eccentricities. It isn't seen in our
Solar System because the orbits of the Sun's planets don't have large enough
eccentricities. Since quite a number of known massive extrasolar planets
follow highly eccentric orbits, asymmetric dust concentrations may be common
features of extrasolar planetary systems. Physical scenarios other than
the resonant interactions of a planet might create a dust peak, like the
recent collision of very large asteroids. For two such major collisions
to happen on opposite sides of Vega at nearly the same time is extremely
unlikely, but it can't be ruled out with the current data.
| Artist's impression of the dust disk
If planets are present, they are unlikely to harbor life. With a mass of
more than 3 solar masses, Vega has a life-expectancy as a main sequence
star of only about 200 million years, which is probably too short to allow
even primitive creatures to evolve.
|| 2.6 Msun
||25.27 light-years (7.751 pc)
||R.A. 18h 36m 56.3s,
Dec. +38° 47' 01"
||3 Lyr, GJ 721, HR 7001,
BD +38°3238, HD 91262,
SAO 67174, HIP 91262
Science fiction connection
A beacon in orbit around Vega was the source of the radio message picked
up by the SETI team in Carl Sagan's novel Contact.