V.3 No 1

59

Chapter 2. Hypothesis of origin of planetary system (part 1)

2.2. Protostar formation

Let us first cite the conventional representation of star condensation by Shklovsky (see Fig. 2.8):

 

fig208.gif (54774 bytes)

 

Fig. 2.8. Different stages of compression of protostellar cloud [1, p. 91, Fig. 27].

 

"1. Several hundred thousand years after the cloud began to compress, and soon after the star-like hot core originated inside the cloud, around this last there arises a dense, optically opaque gas-dust "cocoon" whose interior radius is  equalityalike1.gif (830 bytes)(3 - 5)*1013   cm and exterior equalityalike1.gif (830 bytes)1015   cm. The temperature of the lower layers of "cocoon" is ~500 K - basically, it would be observable as an infrared source. However the cold substance of compressing cloud around the "cocoon" is opaque for infrared rays. The observer will see no "cocoon" inside.

2. Powerful  (equalityalike1.gif (830 bytes)1000Lsunbottom.gif (828 bytes)) infrared radiation from the "cocoon" will press the gas-dust medium of the envelope. By this reason, quite soon (in a few ten thousand years) the compression of envelope will stop the compression of exterior layers of the cloud which after it begins expanding. In this way there originates the exterior gas-dust envelope, or exterior "cocoon" whose radius is  equalityalike1.gif (830 bytes)107 cm. Further both interior and exterior "cocoons" expand. Beginning from some instant of time, the thickness of external "cocoon" will so diminish that we can see through it the infrared radiation of more compact and hot interior "cocoon". Therefore the exterior observer will "see" in infrared rays a compact "hot" source (T equalityalike1.gif (830 bytes)500 K - 1000 K)  surrounded by a more extended and cold  (T equalityalike1.gif (830 bytes)200 K) source. Namely such situation is observed in some cases (e.g., in Orion).

3. Still the gas was ionised only in a small region within the interior "cocoon". The related flow of thermal radio radiation is very small and we are unable to see it. However with the extension, the thickness of interior cocoon becomes so small that the ionising ultraviolet radiation of the protostar passes through it. Thus, in the space of only few thousand years, within the exterior "cocoon" there forms a very compact H II region surrounded by the cold non-ionised gas. At this stage the observer will see a very compact H II region surrounded by the extensive infrared source. Such combination of sources can be observed also quite often.

4. The compact H II region formed in this way fast expands and quite soon achieves the interior boundary of the external "cocoon". The observer will see H II region and infrared source having equal size.

5. After the entire exterior "cocoon" becomes ionised, there forms the compact H II region of the new kind whose mass remains constant and brightness of radio radiation abruptly decreases … The front of ionisation will propagate through the rarefied medium surrounding the cloud, forming with it an usual extensive H II region. The mean lifetime of such H II regions (i.e. the mean lifetime of usual H II clouds) … is about 5*105  years" [1, p. 90- 91].

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