ADS BY GOOGLE
Stars evolve over millions of years. They are born when accumulates a large amount of matter in a the space. The material is compressed and heats up until you start a nuclear reaction, consuming matter, converting it into energy. Small stars spend it slowly and last longer than large ones.
Theories on the evolution of the stars are based on evidence from studies of Spectra related to luminosity. The observations show that many stars are classified as either a regular sequence in which the brightest are the hottest and the smallest, the coldest.
This series of star formed a band known as the main sequence diagram known as a Hertzsprung-Russell Diagram temperatura-luminosidad. Other groups of stars that appear in the diagram include the aforementioned giant and dwarf stars.
The life of a star
The life cycle of a star begins as a great mass of gas relatively cold. The contraction of gas raises the temperature inside the star until reaching 1,000,000 ° C. At this point take place nuclear reactions, whose result is the nuclei of hydrogen atoms are combined with the deuterium to form helium nuclei. This reaction releases large amounts of energy, and stops the contraction of the star. For a while it seems it stabilizes.
But when you end the release of energy, contraction begins again and the temperature of the star returns to increase. Moment begins a reaction between hydrogen, lithium, and other light metals present in the body of the star. New energy is released and the contraction stops.
When lithium and other lightweight materials consumed, contraction resumes and the star enters the final stage of development in which the hydrogen becomes helium at very high temperatures thanks to the catalytic action of carbon and nitrogen. This thermonuclear reaction is characteristic of the main sequence of Star and continues until it consumed all the hydrogen there is.
The star becomes a red giant and reaches its largest size when all its central hydrogen has become helium. If it still shines, the core temperature must rise enough to produce the fusion of helium nuclei. During this process it is likely that the star becomes much smaller and, therefore, more dense.
When it has worn out all possible sources of nuclear energy, it contracts again and becomes a white dwarf. This final stage can be marked by explosions known as "novas". When a star is liberated from its outer exploding like nova or supernova, it returns to the interstellar medium elements heavier than hydrogen that has synthesized inside.
Future generations of stars formed from this material will begin its life with an assortment of elements heavier than previous generations. The star that shed its outer layers in a non-explosive manner become planetary nebulae, old star surrounded by spheres of gas that radiate in a multiple range of wavelengths.
Star to black holeStars with one mass much greater than that of the Sun have a more rapid evolution, of a few million years from his birth to a supernova explosion. The remains of the star can be a neutron star.
However, there is a limit to the size of neutron stars, more than which these bodies are forced to contract until they become a black hole, which can not escape no radiation.Typical stars like the Sun can persist for many billions of years. The final destination of the Dwarfs from low mass is unknown, except that cease to radiate appreciably. It is likely that they become ashes or black dwarfs.
Translation for educational purposes authorized by: Astronomía: Tierra, Sistema Solar y Universo