ciencias

If the spectrum of a star is studied with high-resolution methods can be seen many dark lines at certain wavelengths. These lines are due to light absorption in the deeper layers of atoms of the upper, cooler. The atoms in the star are identified by comparing the stellar absorption lines with those produced in the laboratory by gas known; you can also calculate the temperature and pressure of the atmosphere and the relative abundance of chemical elements. See Fraunhofer lines. Most of the stars are at a stage of its life known as the "main sequence", at this stage, the temperature and luminosity increase with mass. Some stars are brighter and therefore larger than the sequence of the same temperature: the so-called red giant stars. Many stars are weaker and therefore smaller than the sequence of the same temperature, such as white dwarfs (1% of the diameter of the Sun) and neutron stars (0.001% of the diameter of the Sun). Theoretical models of stellar interiors have been calculated based on the theory of balance between the force of gravity, contributing to the collapse of the star, and the pressure of reheated gas, which tend to expand. High temperatures also drive a stellar heat flow from inside to outside the star. For the star is in equilibrium, this heat loss must be offset by the energy released in nuclear reactions internal. As above the various nuclear fuels, the star evolves slowly, and the core shrinks to increasing densities.