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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.
A gas flow then develops from the companion star to the primary. Angular momentum conservation prevents a straight flow from one star to the other and an accretion disk forms instead. Accretion disks surrounding T Tauri stars or Herbig stars are called protoplanetary disks because they are thought to be the progenitors of planetary systems.
Protoplanetary disks and debris disks can be imaged with different methods. If the disk is seen edge-on, the disk can sometimes block the light of the star and the disk can be directly observed without a coronagraph or other advanced techniques (e.g. Gomez's Hamburger or Flying Saucer Nebula [27]).
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.
This is a list of circumstellar disks that have published resolved images. Many of them are protoplanetary disks or debris disks. Only some are transitional disks between protoplanetary and debris. A few disks in this list are circumbinary disks.
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]