Stellar evolution describes a scientific theory of how stars, elements, and galaxies could form spontaneously as a result of the Big Bang, using known physical laws of gravitation and nuclear forces. The theory comes from observing stars at many different stages of existence and comparing with the results of theoretical simulations made by computer models.
The current scientific paradigm for the origin and development of the early universe is the Big Bang theory. This states that the universe originated approximately 13.7 billion years ago from an extremely hot, extremely dense point of extremely small volume. From that point, matter and energy emanated into space – actually, theory says that space itself expanded from that point to become the known visible universe. Slight fluctuations in gravity caused atoms to clump together, eventually forming clusters of matter that would eventually become bonded together by the force of gravitation.
This cloud eventually collapses, releasing heat and condensing into a sphere of superheated gas. The gas reaches the point where nuclear fusion begins, and protons fuse together to form hydrogen, deuterium and helium. A new star is born.
Depending on the size and mass of the star, it may go through various stages of development. The process of fusion continues, creating heavier elements with more protons. At a later stage, the core of the star collapses, forming a neutron star, black hole, supernova, and/or white dwarf star. The explosion releases these heavier elements into space, which can recombine later to form new star systems or objects such as planets. Heavier elements may also be released from non-exploding red giant stars.
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