17.3 L ☉

Fomalhaut ( α Piscis Austrini ) is the brightest star in the constellation of the Southern Fish and the 18th in the list of the brightest stars in the sky. The name means " mouth of the whale " (Arabic فم الحوت fam al - HUT). Other Names: Difda al Auwel, Have orang, Os Piscis Meridiani.

Physical Properties

Fomalhaut is 25 light-years from the Sun. He's like the slightly hotter Wega a main sequence star of spectral type A. Its surface temperature is about 8500 K. It is believed that Fomalhaut is about 100 to 300 million years old. His life is rated at about a billion years.


Fomalhaut is a member of the Castor moving cluster to which, inter alia, Wega is counted. The next member of this movement cluster, TW Piscis Austrini ( a variable star of type BY Draconis ) is only about 0.85 light-years away from Fomalhaut and has a very similar proper motion.

The two stars appear to be weakly gravitationally bound, but probably make no double star system. It is believed that such movement heap had a common origin as clusters of low density.

Dust disk and exoplanet

Fomalhaut is surrounded by a dust disk with a diameter of around 40 billion kilometers. The center of the disc does not coincide with the star, but is about 15 astronomical units ( AU) of Fomalhaut away. Therefore a planet at a distance of about 7.4 bis 10.5 billion kilometers It has been suggested to the star.

The dust disk is a ring structure of which was believed to be caused by the gravity of a planet. The infrared radiation of the disc could be observed already in the 1980s by the Infrared Astronomical Satellite ( IRAS ), NASA. The dust disk is inside sharply demarcated from the main star at a distance of about 133 AU and itself has a width of about 25 AU.

The exoplanet orbiting the central star at an average distance of about 115 AU within the inner edge of the torus. Due to the eccentricity of the orbit of 0.11 varies the distance 102-128 AE and currently stands at about 119 AU.

The scale in the bottom left image has a length of 100 AU or 13 " for comparison. Significantly limited the diffraction disk of Fomalhaut in the picture at the top has a diameter of 130 ".