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In astronomy, stellar evolution refers to the changes which stars undergo during their lifetime. Stars change in color, luminosity, size and temperature through their lifespan. Scientist can not study an individual stars lifetime though because they far exceed ours and therefore we must study stellar evolution by observing the life cycle of numerous stars, each at a different point in its life cycle, and then running computer models which simulate the structure of stars.
Through history stars have been recorded, starting with the brightest, which have been named going back as far as 1000 b.c. by the chinese. Today we name stars in three categories, the first being the brightest are named for what constellation they are in. Variable stars are the ones that change in luminosity periodically and the fainter stars are logged in the Henry Draper Catalogue under numubers like HD 12938. Stars exist either alone or in groups of two or more in a system or cluster. Large clusters are grouped into galaxies and in our Galaxy, the Milky Way there are more than 100 billion stars. There are also 10's of millions of galaxies that are part of the known universe. Think about that and tell me there's no life out there.
As technology permitted it was found that stars positions are not fixed and that stars move at various speeds measured in changes of direction in fractions of a second of arc per year. This second of arc is the angular size of a pinhead that is 183 m away (wow, now thats precise, you would think). Many of the fainter stars almost seem to not move at all though because they are so far away and thats why we use them as reference stars to measure others and scientists call this proper motion. A Parallex is another apparent m...
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...rs of a fraction of a second. Its neutrinos send a shockwave out blasting most of the stars materials into space, but many of the elements get caught up in neutrinos and combine to create heavier elements. Without supernovae there would be no heavier elements than Iron-56.
It is not understood well, but in some supernovae the gravity is so intense within the red supergiant that the electrons are forced into the atomic nuclei where they combine with protons to form neutrons. The electromagnetic forces keeping apart the seperate nuclei are gone and the entire core becomes a dense ball of neutrons or an atomic nucleus about the size of Manhatten called a Neutron Star. If the mass is great enough though, when the star turns into a red supergiant it will collapse under its on gravity into a radius smaller than the Schwarzchild Radius and turn into a Black Hole.
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