Astrophysics (index)about

protoplanetary disk

(PPD, planetary disk, proto-planetary disk, preplanetary disk, PP disk, disk)
(disk of dust and gas around a young star or protostar)

A protoplanetary disk (aka preplanetary disk, either abbreviated PP disk or PPD) is a circumstellar disk, consisting of dust and gas orbiting a young star or protostar such as a T-Tauri star. Radii can be as much as 1000 AU. Such disks are thought to provide the material for planet formation. The disks often develop a flared torus shape due to a combination of heat and radiation pressure from the central star. They can last several million years, evolving through accretion, outflows, photoevaporation, and/or condensation into larger bodies, small to large (planetesimals or planets). Though it is millions of years, this is short enough that it has been considered as a possible limiting factor in the type of planets emerging, e.g., how large a gas planet can grow, since the gas portion of the disk disappears.

The term proplyd is used for observed protoplanetary disks, visible for being illuminated, typically by the star's ultraviolet radiation, resulting in photodissociation, ionization, and velocity dispersion.

Protoplanetary disks are also detected through an infrared excess: disk material such as dust heated by the protostar produces black-body radiation at a lower temperature range. Some have been observed in silhouette due to glowing nebulae behind them, e.g., the Orion Disks. Direct imaging of such disks have been carried out by the Hubble Space Telescope, Atacama Large Millimeter Array, and Subaru Telescope.

The dust in a protoplanetary disk necessarily varies in size if solid objects are to form. The dust inherited from the star-forming region is presumed to be up to micron sized. Some information about the location of different sizes can be gleaned from resolving it at different wavelengths: grains tend to emit thermal radiation most efficiently at a wavelength on the order of their diameter. Disks generally show fewer larger grains further out which matches the notion that the effects of radiation pressure on dust grains are significant.


(disks,object type)
http://en.wikipedia.org/wiki/Protoplanetary_disk

Referenced by:
accretion
atmosphere formation
baroclinicity
barrier
bouncing barrier
carbon planet
circumstellar disk
cold mass accretion (CMA)
carbon monoxide (CO)
computational astrophysics
core accretion model
cosmic dust
debris disk
direct imaging
radial-drift barrier
dynamical instability
dynamo
electrostatic barrier
Elias 2-27
fragmentation barrier
FU Orionis star (FUor)
gas flow
gravitational instability (GI)
gravitational instability model
HL Tau
hydrostatic equilibrium
I band
Infrared Space Observatory (ISO)
Kelvin-Helmholtz instability (KHI)
kilometer size barrier
meter size barrier
nebular hypothesis
1.3mm observation
Orion Disks
passive dust
photoevaporation
planetary embryo
planetary migration
planet formation
polarimetry
vortensity (PV)
RODEO
Rossby waves
Rossby wave instability (RWI)
snow line
solar nebula
speckle suppression
spiral density wave
stellar age determination
striae
Toomre Q parameter (Q)
T-Tauri star (TTS)
TW Hydrae (TW Hya)

index