SELF

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O.N. Karavashkina and S.B. Karavashkin

Formation of the region of ionised gas, about which Shklovsky said in the item 3 of above citation, is actually the key issue for the protostellar radiation at this stage of evolution. Until the compact region of ionised hydrogen is unformed and unstable, the protostar radiation will be weak. Only when the convection in the exterior layer of protostar becomes stable and due to it the outside energy transfer stabilises, we will see an abruptly growing lightening (see Fig. 2.8.5).

Fig. 2.8.5

The photograph of this stage is shown in Fig. 2.11.

Fig. 2.11. The star-forming region in the galaxy 2366. The protostar in the centre of cloud sharply distinguishes from other stars by its bright luminosity. Copied from  http://www.ifa.hawaii/research

And finally in Fig. 2.8.6 we see the young star in the aureole of cloud which at this stage of finishing formation often goes on still to fall to the centre of practically having been formed young star.

Fig. 2.8.6

Shklovsky applied his model to the Sun and tracked, how it could form (see Fig. 2.12).

Fig. 2.12. Theoretical plot of protostellar radius against time [1, p. 88, Fig. 25].

"In Fig. 2.12 we show schematically the dependence of radius of a protostar whose initial mass was equal to the Sun mass, with respect to time. To have a scale, the horizontal broken lines correspond to the radii of planets of Solar system. We see that in the beginning of "free-fall stage" of the protostar compressing under affection of its own gravity and not so long ago being a dense, cold "molecular" cloud, the radius of protostar is close to that of Pluto orbit. With it the mean concentration of particles (mainly hydrogen molecules) was 10¹² cm ^{- 3} . The free-fall stage (begun from such density) lasts some more than 10 years … During this short time the protostar compresses till the Mercury orbit, i.e. approximately in 100 times. Of course, essentially longer period of compression preceded to this stage when the cloud with the initial density 10 ⁵ - 10 ⁶ cm ^{- 3} compressed to the Pluto orbit. Further, the protostar compression decelerates, as it becomes opaque to its own radiation. In the life of protostar enveloped by convection the "Hayashi stage" begins. In the very beginning of this stage there has to be the "flash" … In a few ten million years, the protostar compression will almost stop and it will "settle" onto the main sequence" [1, p. 87- 88].

We would only mention one illogic moment in this picturesque description: Shklovsky attributes the beginning of thermonuclear reactions to the today radius of Sun, while we will see below, at that time the Sun radius was much more. We do not give here our own quantitative estimations, as the aim of this chapter is only to understand the mechanism of planets origin. In the chapter 3, where we build the model of protoplanet, we will give the dynamics of its size change, and illustratively - dynamics of some parameters for the Sun.

The lower series of pictures in Fig. 2.8 shows us, dependently on the initial mass of protostar cloud, that free fall of gas can go on even when the star has flashed and formed as the whole. This highly important peculiarity, individual for each star, predestines the entire course of its further evolution. In particular, the diagram 2.12 has been calculated for an ideal case, when the mass of protostar cloud was strongly balanced and the process of energy accumulation goes in full correspondence with the process of thermodynamic stabilisation of the core of forming star. But it is understandable, they far from always are in such agreement, and when the mass of compressing cloud was excessive, the thermonuclear reactor can initiate already at the stage of "free fall". This will strongly change the whole course of the star evolution. The peculiarities of this branch of evolution are quite interesting per se and can in some cases exclude in future the protoplanet nebula formation. Below we will consider this branch in more details, but here let us first consider the quiet way of process.