D E B R I S D I S K S VI

Fomalhaut and Vega

Hubble Space Telescope image of the debris ring surrounding Fomalhaut

The blue-white star Fomalhaut, located at distance of 7.7 parsecs (25 light years), has an unusually well defined debris ring. Its collisional dust is described as amorphous silicate and carbonaceous grains. The ring's extensive central clearance has long suggested the existence of one or more giant planets orbiting inside. These hints have recently been confirmed through direct photographic imaging of a gas giant located just inside the ring's inner edge, at an astrocentric radius of about 100 AU. Considering that the Solar System's outermost planet, Neptune, orbits at a semimajor axis of 30 AU, the Fomalhaut system could accommodate four concentric versions of our own eight-planet ensemble.

K.Y.L. Su and colleagues describe Fomalhaut's ring as quiescent, with no major collisions during the past several million years (Su et al. 2005b). See also Rings.

Spitzer Space Telescope image of the debris disk around Vega

The blue-white star Vega, located at distance of 7.8 parsecs (25 light years), may be a sibling to Fomalhaut. Vega is surrounded by an even more prominent ring of dusty debris, which we view in a pole-on orientation. This infrared image by the Spitzer Space Telescope is the best picture so far obtained, representing a structure whose diameter is more than 400 AU.

The star itself is invisible because of photosphere subtraction in the imaging process. The white circle at the center of the image represents the disk's central clearance, which extends to a radius of about 86 AU. Most of the debris is concentrated between 86 and 200 AU. Given the large volume of dust in the system, K.Y.L. Su and colleagues attribute its production to recent catastrophic collisions among large planetoids (Su et al. 2005a). Image courtesy NASA/JPL-Caltech/Spitzer Space Telescope/KYL Su et al.