Definitions

Debris disks

Debris disk

A debris disk is a ring-shaped circumstellar disk of dust and debris in orbit around a star. Debris disks have been found around both evolved and young stars, as well as at least one debris disk in orbit around a neutron star. They can constitute a phase in the formation of a planetary system following the protoplanetary disk phase. They can also be produced and maintained as the remnants of collisions between planetismals.

By 2001, over 900 candidate stars have been found to possess a debris disk. They are usually located by examining the star system in infrared light and looking for an excess of radiation beyond that emitted by the star. This excess is inferred to be radiation from the star that has been absorbed by the disk, then radiated away as infrared energy.

In certain cases the debris disks can be observed directly by occulting the primary star and then imaging the system.

Observation history

In 1984 a debris disk was located in orbit around the star Vega using the IRAS satellite. Initially this was believed to be a protoplanetary disk, but it is now thought to be a debris disk due to the lack of gas in the disk. Subsequently irregularities have been found in the disk, which may be indicative of the presence of planetary bodies. Similar discoveries of debris disks were made around the stars Fomalhaut and Beta Pictoris.

By 1998 a debris disk had been located around the nearby star 55 Cancri, a system that is also known to contain a planet. Structures in the debris disk around Epsilon Eridani also suggest perturbations by a planetary body in orbit around that star, which may be used to constrain the mass and orbit of the planet.

Origin

Typical debris disks contain small grains 1–100 μm in size. Radiation from the host star can cause these particles to spiral inward because of the Poynting-Robertson effect, so the lifetime of the disk will be on the order of 10 Myr or less. Thus, for a disk to remain intact, a process is needed to continually replenish the disk. This can occur, for example, by means of collisions between larger bodies. This can occur on a continual basis as collisions grind objects down into ever smaller bodies.

For collisions to occur in a debris disk, the bodies must be gravitationally perturbed sufficiently to create relatively large collisional velocities. A planetary system around the star can cause such perturbations, as can a binary star companion or the close approach of another star.

Known belts

Belts of dust or debris have also been detected around stars other than the Sun, including the following:

Star Spectral
class
Distance
(ly)
Orbit
(AU)
Epsilon Eridani K2V 10.5 35–75
Tau Ceti G8V 11.9 35–50
Vega A0V 25 86–200
AU Microscopii M1Ve 33 50–150
HD 69830 K0V 41 <1
55 Cancri A G8V 41 27–50
Pi1 Ursae Majoris G1.5Vb 46.5 ?
HD 139664 F5IV-V 57 60–109
Eta Corvi F2V 59 100–150
HD 53143 K1V 60 ?
Beta Pictoris A5V 63 25–550
Zeta Leporis A2Vann 70 2–8
HD 92945 K1V 72 45–175
HD 107146 G2V 88 130
Fomalhaut A3V 133 25
HD 12039 G3-5V 137 5
HD 15115 F2V 150 315–550
HR 4796 A A0V 220 200
HD 141569 B9.5e 320 400
HD 113766 A F4V 430 0.35–5.8

The orbital distance of the belt is an estimated mean distance or range, based either on direct measurement from imaging or derived from the temperature of the belt. The Earth has an average distance from the Sun of 1 AU.

See also

References

External links

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