Debris disk

The first four debris disks discovered with IRAS are known as the "fabulous four": Vega, Beta Pictoris, Fomalhaut, and Epsilon Eridani.

Subsequently, direct images of the Beta Pictoris disk showed irregularities in the dust, which were attributed to gravitational perturbations by an unseen exoplanet.

[6] Other exoplanet-hosting stars, including the first discovered by direct imaging (HR 8799), are known to also host debris disks.

The nearby star 55 Cancri, a system that is also known to contain five planets, also was reported to have a debris disk,[7] but that detection could not be confirmed.

During the formation of a Sun-like star, the object passes through the T-Tauri phase during which it is surrounded by a gas-rich, disk-shaped nebula.

The nebula continues to orbit the pre-main-sequence star for a period of 1–20 million years until it is cleared out by radiation pressure and other processes.

At some point during their lifetime, at least 45% of these stars are surrounded by a debris disk, which then can be detected by the thermal emission of the dust using an infrared telescope.

Collisions will grind down these grains to sub-micrometre sizes, which will be removed from the system by radiation pressure from the host star.

This can occur, for example, by means of collisions between larger bodies, followed by a cascade that grinds down the objects to the observed small grains.

[13] For collisions to occur in a debris disk, the bodies must be gravitationally perturbed sufficiently to create relatively large collisional velocities.

Infrared spectra with Spitzer have shown that the dust is dominated by small particles made up of silicates that have a size between sub-μm and a few μm.

[17] In rare cases the dust cloud can orbit in front of the star, causing dips of brightness in the optical.