Protoplanetary disk

A protoplanetary disk is a rotating

Formation

It is now a T Tauri star. Accretion of gas onto the star continues for another 10 million years,[6] before the disk disappears, perhaps being blown away by the young star's stellar wind, or perhaps simply ceasing to emit radiation after accretion has ended. The oldest protoplanetary disk yet discovered is 25 million years old.^[7][8]

Protoplanetary disks around T Tauri stars differ from the disks surrounding the primary components of close binary systems with respect to their size and temperature. Protoplanetary disks have radii up to 1000

Protoplanetary disks have been observed around several young stars in our galaxy. Observations by the Hubble Space Telescope have shown proplyds and planetary disks to be forming within the Orion Nebula.^[10][11]

Protoplanetary disks are thought to be thin structures, with a typical vertical height much smaller than the radius, and a typical mass much smaller than the central young star.^[12]

The mass of a typical proto-planetary disk is dominated by its gas, however, the presence of dust grains has a major role in its evolution. Dust grains shield the mid-plane of the disk from energetic radiation from outer space that creates a dead zone in which the magnetorotational instability (MRI) no longer operates.^[13][14]

It is believed that these disks consist of a turbulent envelope of plasma, also called the active zone, that encases an extensive region of quiescent gas called the dead zone.^[14] The dead zone located at the mid-plane can slow down the flow of matter through the disk which prohibits achieving a steady state.

Supernova remnant ejecta producing planet-forming material.

Planetary system

The

Some of the moons of

Debris disks

Gas-poor disks of circumstellar dust have been found around many nearby stars—most of which have ages in the range of ~10 million years (e.g.

Based on recent

• 
  Illustration of the dynamics of a proplyd
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  20 protoplanetary discs captured by the High Angular Resolution Project (DSHARP).^[21]
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  A shadow is created by the protoplanetary disc surrounding the star HBC 672 within the nebula.^[22]
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  Protoplanetary disc

  Ophiuchus star-forming region.^[23]
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  Protoplanetary disk HH 212.^[24]
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  By observing dusty protoplanetary discs, scientists investigate the first steps of planet formation.^[25]
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  Concentric rings around young star

  HD 141569A, located some 370 light-years away.^[26]
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  Debris disks detected in HST images of young stars, HD 141943 and HD 191089 - images at top; geometry at bottom.^[27]
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  Protoplanetary disk

  stellar jet

  .
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  Artist's impression of a protoplanetary disk.
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  A proplyd in the Orion Nebula.
• Video shows the evolution of the disc around a young star like HL Tauri (artist concept).
• 
  Image of the circumtrinary disc around GW Orionis.^[28]
• 
  An artist's concept of a protoplanetary disk

See also

Wikimedia Commons has media related to Protoplanetary disks.

References