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A protoplanetary disk is a rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may not be considered an accretion disk ; while the two are similar, an accretion disk is hotter and spins much faster.
An accretion disk is a structure (often a circumstellar disk) formed by diffuse material [a] in orbital motion around a massive central body. The central body is most frequently a star . Friction , uneven irradiance, magnetohydrodynamic effects, and other forces induce instabilities causing orbiting material in the disk to spiral inward toward ...
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.
ALMA image of HL Tauri, a protoplanetary disk. In astrophysics, accretion is the accumulation of particles into a massive object by gravitationally attracting more matter, typically gaseous matter, into an accretion disk. [1] [2] Most astronomical objects, such as galaxies, stars, and planets, are formed by accretion processes.
In astronomy, a disk wind is a particle outflow observed around accretion disks, mainly near protoplanetary disks [1] [2] and active galactic nulei (AGN). [3] [4] The disk wind is made up of a gaseous and a dusty component. [1] Especially in edge-on protoplanetary disks this disk wind can be directly imaged. [5] [6]
The protoplanetary disk is sometimes referred to as an accretion disk, because while the young T Tauri-like protostar is still contracting, gaseous material may still be falling onto it, accreting on its surface from the disk's inner edge. [40] In an accretion disk, there is a net flux of mass from larger radii toward smaller radii. [23]
2MASS J04202144+2813491 (also known as Tau 042021) [3] [6] is an edge-on protoplanetary disk in the Taurus Molecular Cloud. [3]The star is hidden behind the edge-on disk. Early estimates found that it has a mass of 0.272 ±0.009 M ☉, [7] but a later study did find a higher mass of 0.3–0.4 M
Disk Planet Planet distance (in AU) Notes HD 100546: Disk extends out to 17: Diameter, 721 AU [1] HD 100546 b: 6.5 – GM Aurigae: 0–300 – – – Disc is warped Lynds 1551: 0.1 – – – Binary system 45 AU apart OTS 44 – – – – Second smallest brown dwarf TW Hydrae: 80: 440 [2]