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There are two main forces acting in a star: Gravitational contraction: it is due to the higher layers, this force pushes mass to the center. Radiation pressure: it is produced by the inner layers, and it forces material upwards.
This guide illustrates in a general way how stars of different masses evolve and whether the final remnant will be a white dwarf, neutron star, or black hole. Stellar evolution gets even more complicated when the star has a nearby companion.
Polytropic Stellar Models. A proper understanding of stellar structure draws on many different areas of physics,e.g., thermonuclear reactions, the atomic physics of stellar opacity, etc. However, we can go a good bit further using the principles of hydrostatic equilibrium.
Understanding the evolution of stars help astronomers to understand: The nature and future fate of our Sun. The origin of our solar system. How we compare our solar system with other planetary systems. If there could be life elsewhere in the universe. Properties of the Sun: the nearest star. and how astronomers measure them – important!
One of our goals in this class is to be able to describe not just the observ-able, exterior properties of a star, but to understand all the layers of these cosmic onions — from the observable properties of their outermost layers to the physics that occurs in their cores.
A star’s life is all about trying to maintain hydrostatic equilibrium, or a balance between the force of gravity trying to contract the star and the pressure generated by the heat released in nuclear fusion in the star’s interior.
Stars form when a particular type of interstellar cloud, called a molecular cloud, starts collapsing by the effect of its own gravity and breaks up into tens or hundreds of smaller clumps. Owing to the gravitational attraction, each cloud fragment attracts more and more matter from its surroundings (see Figure 1).
