Young Stars

   If the birth of stars can be described by a single, then a further way of development of the star is almost entirely dependent on mass, and only at the very end may play a role of chemical composition.

   Young stars of low mass

   Young stars of low mass (up to three solar masses), are approaching the main sequence, is fully convective. This is indeed protozvezdy, in the center of which is only just starting the nuclear reaction, and all the radiation was mainly due to the gravitational compression. That is the star luminosity is increasing with the constant effective temperature. And Gertsshprunga-Russell diagram, we see a nearly vertical track, called track Hayashi. As the young star to the main sequence contraction slows. Objects of this type are associated with stars of type ? Taurus.

   At this time, for the mass of stars more than 0.8 solar masses, the nucleus becomes transparent to radiation, and prevail radiant energy transfer in the nucleus, and the top shell is convective. What came to the main sequence stars of lesser mass, significantly, no one knows, because the time spent in the discharge of these young stars exceeds the age of the universe. All our ideas about the evolution of these stars stick to numerical calculations.

   As compression of the star begins to rise the pressure of degenerate electron gas, and at some radius of the stars this pressure stops the growth of the central temperature, and then it starts to depress. And for the stars is less than 0.08 this proves fatal: exuding energy during nuclear reactions will never be enough to cover the costs of radiation. Such under-the stars are called brown dwarfs, and their fate - a constant pressure, while the degenerate gas pressure will not stop it, and then - a gradual cooling to stop all nuclear reactions.

   The young stars of intermediate mass

   The young stars of intermediate mass (from 2 to 8 solar masses) evolve qualitatively in the same way as their smaller sisters, except that there is no convection zone up to the main sequence.

   Objects of this type are associated with the Sc. stars Ae \ Be Herbita irregular variables of spectral type B-F5. They also observed disks bipolar jets. The rate of expiration, luminosity and effective temperature is significantly greater than for ? Taurus, so they efficiently heat and scatter the remnants protozvezdnogo clouds.

   Young stars with mass greater than 8 solar masses

   In fact, this is normal star. While the accumulated weight of the hydrostatic core, the star managed to slip all the intermediate stage and the heat of nuclear reactions to such an extent that they compensate for the loss of radiation. In these stars the expiration of the mass and luminosity is so high that not only stops kollapsirovanie remaining external areas, but pushing them back. Thus, the mass of stars formed considerably less weight protozvezdnogo clouds. Probably this explains the lack of stars in our galaxy more than 100-200 solar masses.