Protostar

Source: Wikipedia, the free encyclopedia.
For other uses, see Protostar (disambiguation).
Star formation
Object classes
Theoretical concepts

A protostar is a very young

main-sequence star at the onset of hydrogen fusion
producing helium.

History

The modern picture of protostars, summarized above, was first suggested by Chushiro Hayashi in 1966.[3] In the first models, the size of protostars was greatly overestimated. Subsequent numerical calculations[4][5][6] clarified the issue, and showed that protostars are only modestly larger than main-sequence stars of the same mass. This basic theoretical result has been confirmed by observations, which find that the largest pre-main-sequence stars are also of modest size.

Protostellar evolution

Infant star CARMA-7 and its jets are located approximately 1400 light-years from Earth within the Serpens South star cluster.[7]
Main article: Star formation

Star formation begins in relatively small

gas pressure and magnetic pressure, which tend to inflate it. As the dense core accrues mass from its larger, surrounding cloud, self-gravity begins to overwhelm pressure, and collapse begins. Theoretical modeling of an idealized spherical cloud initially supported only by gas pressure indicates that the collapse process spreads from the inside toward the outside.[9] Spectroscopic observations of dense cores that do not yet contain stars indicate that contraction indeed occurs. So far, however, the predicted outward spread of the collapse region has not been observed.[10]

Illustration of the dynamics of a proplyd

The gas that collapses toward the center of the dense core first builds up a low-mass protostar, and then a protoplanetary disk orbiting the object. As the collapse continues, an increasing amount of gas impacts the disk rather than the star, a consequence of angular momentum conservation. Exactly how material in the disk spirals inward onto the protostar is not yet understood, despite a great deal of theoretical effort. This problem is illustrative of the larger issue of accretion disk theory, which plays a role in much of astrophysics.

HBC 1 is a young pre-main-sequence star.[11]

Regardless of the details, the outer surface of a protostar consists at least partially of shocked gas that has fallen from the inner edge of the disk. The surface is thus very different from the relatively quiescent

hydrogen-1 is not yet fusing with itself. Theory predicts, however, that the hydrogen isotope deuterium (hydrogen-2) fuses with hydrogen-1, creating helium-3. The heat from this fusion reaction tends to inflate the protostar, and thereby helps determine the size of the youngest observed pre-main-sequence stars.[12]

The energy generated from ordinary stars comes from the nuclear fusion occurring at their centers. Protostars also generate energy, but it comes from the radiation liberated at the shocks on its surface and on the surface of its surrounding disk. The radiation thus created must traverse the

interstellar dust in the surrounding dense core. The dust absorbs all impinging photons and reradiates them at longer wavelengths. Consequently, a protostar is not detectable at optical wavelengths, and cannot be placed in the Hertzsprung–Russell diagram, unlike the more evolved pre-main-sequence
stars.

The actual radiation emanating from a protostar is predicted to be in the infrared and millimeter regimes. Point-like sources of such long-wavelength radiation are commonly seen in regions that are obscured by molecular clouds. It is commonly believed that those conventionally labeled as Class 0 or Class I sources are protostars.[13][14] However, there is still no definitive evidence for this identification.

Observed classes of young stars

For details of observational classification, see Young stellar object.
Class peak emission duration (years)
0 submillimeter 104
I far-infrared 105
II near-infrared 106
III visible 107[15]

Gallery

  • Video about the protostar V1647 Orionis and its X-ray emission (2004).
  • Protostar outburst - HOPS 383 (2015).
    Protostar outburst - HOPS 383 (2015).
  • Protostar in Herbig-Haro 46/47.
    Protostar in Herbig-Haro 46/47.
  • A protostar inside a Bok globule (Artist's image).
    A protostar inside a Bok globule (Artist's image).
  • Stellar cluster RCW 38, around the young star IRS2, a system of two massive stars and protostars.
    Stellar cluster RCW 38, around the young star IRS2, a system of two massive stars and protostars.
  • Structures of dust forming around a protostar (in the central pink line) in nebula L1527 (2022).
    Structures of dust forming around a protostar (in the central pink line) in nebula L1527 (2022).

See also

References

  1. ISBN 3-527-40559-3
    .
  2. S2CID 89604015
    .
  3. doi:10.1146/annurev.aa.04.090166.001131
    .
  4. doi:10.1093/mnras/145.3.271
    .
  5. doi:10.1086/157734
    .
  6. doi:10.1086/158377.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  7. ^ "Infant Star's First Steps". Retrieved 10 November 2015.
  8. doi:10.1086/160780
    .
  9. doi:10.1086/155274
    .
  10. S2CID 16270619.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  11. ^ "A diamond in the dust". Retrieved 16 February 2016.
  12. doi:10.1086/166694
    .
  13. hdl:2060/19870005633.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  14. doi:10.1086/172425.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  15. ^ "IMPRS" (PDF). www.solar-system-school.de.

External links

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