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Circumstellar disc

A circumstellar disc (or circumstellar disk) is a torus, pancake or ring-shaped accretion disk of matter composed of gas, dust, planetesimals, asteroids, or collision fragments in orbit around a star. Around the youngest stars, they are the reservoirs of material out of which planets may form. Around mature stars, they indicate that planetesimal formation has taken place, and around white dwarfs, they indicate that planetary material survived the whole of stellar evolution. Such a disc can manifest itself in various ways.

The is a reservoir of small bodies in the Solar System located between the orbit of Mars and Jupiter. It is a source of interplanetary dust.

asteroid belt

beyond the orbit of Neptune

Edgeworth-Kuiper belt

beyond the orbit of Neptune

Scattered disc

; only the inner Oort cloud has a toroid-like shape. The outer Oort cloud is more spherical in shape.

Hills cloud

Circumprimary disc is one which orbits the primary (i.e. more massive) star of the binary system. This type of disc will form through accretion if any angular momentum is present in the infalling gas.[4]

[4]

Circumsecondary disc is one which orbits around the secondary (i.e. less massive) star of the binary star system. This type of disc will only form when a high enough level of angular momentum is present within the infalling gas. The amount of angular momentum required is dependent on the secondary-to-primary mass ratio.

disc is one which orbits about both the primary and secondary stars. Such a disc will form at a later time than the circumprimary and circumsecondary discs, with an inner radius much larger than the orbital radius of the binary system. A circumbinary disc may form with an upper mass limit of approximately 0.005 solar masses,[5] at which point the binary system is generally unable to perturb the disc strongly enough for gas to be further accreted onto the circumprimary and circumsecondary discs.[4] An example of a circumbinary disc may be seen around the star system GG Tauri.[6]

Circumbinary

Given the formation of a circumbinary disc, the formation of an inner cavity surrounding the binary is inevitable. This cavity is the result of spiral density waves located at , specifically the outer Lindblad resonances. The exact resonances which excise the cavity depend on the eccentricity of the binary , but in each case the size of the cavity is proportional to the binary separation .[7]

Lindblad resonances

consist of planetesimals along with fine dust and small amounts of gas generated through their collisions and evaporation. The original gas and small dust particles have been dispersed or accumulated into planets.[14]

Debris discs

or interplanetary dust is the material in the Solar System created by collisions of asteroids and evaporation of comet seen to observers on Earth as a band of scattered light along the ecliptic before sunrise or after sunset.

Zodiacal cloud

is dust around another star than the Sun in a location analogous to that of the Zodiacal Light in the Solar System.

Exozodiacal dust

: In this stage large quantities of primordial material (e.g., gas and dust) are present and the discs are massive enough to have potential to be planet-forming.

Protoplanetary discs

Transition discs: At this stage, the disc shows significant reduction in the presence of gas and dust and presents properties between protoplanetary and debris discs.

: In this stage the circumstellar disc is a tenuous dust disc, presenting small gas amounts or even no gas at all. It is characterized by having dust lifetimes smaller than the age of the disc, hence indicating that the disc is second generation rather than primordial.

Debris discs

Stages in circumstellar discs refer to the structure and the main composition of the disc at different times during its evolution. Stages include the phases when the disc is composed mainly of submicron-sized particles, the evolution of these particles into grains and larger objects, the agglomeration of larger objects into planetesimals, and the growth and orbital evolution of planetesimals into the planetary systems, like our Solar System or many other stars.


Major stages of evolution of circumstellar discs:[16]

McCabe, Caer (May 30, 2007). . NASA JPL. Retrieved 2007-07-17.

"Catalog of Resolved Circumstellar Disks"

(from Paul Kalas, "Circumstellar Disk Learning Site)"

Image Gallery of Dust disks