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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.
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]
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
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 ...
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 the inner disk, the planet spirals inward on the viscous timescale, following the accretion of gas onto the star. In this case, the migration rate is typically slower than would be the migration of the planet in the Type I regime. In the outer disk, however, migration can be outward if the disk is viscously expanding.
The accretion disk of the protostar IRAS 16293-2422 has parts rotating in opposite directions. This is the first known example of a counterrotating accretion disk. If this system forms planets, the inner planets will likely orbit in the opposite direction to the outer planets. [35]
Artist's conception of a protoplanetary disk. The Solar System is believed to have formed according to the nebular hypothesis, first proposed in 1755 by Immanuel Kant and independently formulated by Pierre-Simon Laplace. [2] This theory holds that 4.6 billion years ago the Solar System formed from the gravitational collapse of a giant molecular ...