THE STARS
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The stars are big bodies consist primarily of hydrogen, where they develop strong gravitational forces such as to give rise to nuclear fusion processes. The stars are born from gravitational contraction of interstellar clouds calls protostars emitting infrared. When nuclear fusion processes trigger, the star begins to issue in all directions radiation wavelengths and particles becoming visible over great distances. Its brightness in the sky depends on its intrinsic characteristics (size, state of its lifecycle, ...) and its distance from the Earth. The nearest star is Proxima Centaurus 4.2 light-years away. The size of diameters can also be 1000 times that of the Sun but most are similar to the Sun. Every star has its own emission spectrum characteristic (trend of emission intensity at different wavelengths) which gives us a lot of informations on its composition.

  

All the stars have their own life cycle, are born, die, and from their remains new stars and other celestial bodies will born . The main loop takes about 10 billion years, the Sun is 4.5 billion years. Since during the fusion it's consumed the hydrogen of stellar nucleus, processes begin that transform the star into a red giant, then in a planetary nebula and finally into a white dwarf which will definitely becoming a black dwarf. If the stellar mass was at least 10 times that of the Sun, the star ended the cycle of hydrogen and helium, contracts and rotates so fast to cause the emissions of hundreds very regular pulses per second becoming a pulsar. The biggest stars will give rise to supernovae, that explode and form a Nebula with irregular contours. At the center of the Nebula there is a neutron nucleus or a black hole if the star's original mass was 30 times that of the Sun. The black hole exerts gravitational action so strong that nothing can escape, even light , so that they are invisible. The stars may be single or in pairs called binaries or groups of stars called Clusters that orbit around their center of mass. The star novae manifested a sudden increase in brightness for a time before returning to previous brightness. Spent a period of time this phenomenon can repeat as well as astronomers have already observed. Novae are almost all binary stars.

 

             Star Nebula V838 Monocerontis

  

                    Globular cluster 47 Tucanae heic o616e

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