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Star formation
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see
Star formation
'''Star formation''' is the process by which hydrogen & helium in
molecular clouds change into the ball of
Plasma (physics) plasma we call a
star.
According to current theories of star formation, cores of molecular clouds (regions of especially high density) become gravitationally unstable, fragment and begin to
gravitational collapse collapse (sometimes, shockwaves from
supernovae will trigger star formation in nearby gas clouds). Part of the gravitational energy lost in this collapse is radiated in the
infrared, with the remainder increasing the temperature of the core of the object. The accretion of material happens partially through a
circumstellar disc. When the density and temperature are high enough,
deuterium Nuclear fusion fusion ignition occurs, and the outward
Radiation pressure pressure of the resultant radiation slows (but does not stop) the collapse. Material the cloud continues to "rain" onto the
protostar. In this stage bipolar flows are produced, probably an effect of the
angular momentum of the infalling material. Finally,
hydrogen begins to fuse in the core of the star, and the rest of the enveloping material is cleared away.
The stages of the process are well defined in stars with masses around one
solar mass or less. In high mass stars, the length of the star formation process is comparable to the other timescales of their evolution, much shorter, and the process is not so well defined.
The later evolution of stars are studied in
stellar evolution.
Observations
Key elements of star formation are only available by observing in
wavelengths other than the
optical astronomy optical. The structure of the molecular cloud and the effects of the protostar are best observed in
rotational transition rotational transitions of
Carbon monoxide CO and other molecules; these are observed in the millimeter and
radio astronomy submillimeter range. The radiation from the protostar and early star has to be observed in
infrared infrared astronomy wavelengths, the
extinction caused by the rest of the cloud where it is being formed is usually too big to allow us to observe it in the visual part of the spectrum.
The formation of individual stars can only be directly observed in
Milky Way our Galaxy, but in distant galaxies star formation has been detected through its unique
Gas_chromatography-Mass_spectrometry spectral signature.
References & Further reading
The theory of collapse of gas under its own gravity was developed by
Jeans mass Jeans and although the theory does not treat many phenomena known to be important it is a very useful and widely used first approximation. The original paper is available free of charge (to participating institutions):
* J. H. Jeans. Philosophical Transactions of the Royal Society of London. Series A, Containing Papers of a Mathematical or Physical Character, Vol. 199. (1902), pp. 1-53. Stable URL: [http://links.jstor.org/sici?sici=0264-3952%281902%29199%3C1%3ATSOASN%3E2.0.CO%3B2-H]
{{Astronomy-footer}}
Category:Stellar evolution
et:Täheteke
es:Formación estelar
fr:Naissance des étoiles
it:Formazione stellare
ms:pembentukan bintang
nl:Stervorming
pl:Powstawanie gwiazd
pt:Formação estelar
sk:Vznik hviezdy
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