The Birth of Arcturus Arcturus was formed in the halo of the Milky Way. It was formed about 10 billion years ago, in a generation of star formation prior to that in which our sun was formed. Parcels within a giant molecular cloud experienced a gravitational pull towards each other. As the cloud collapsed, the denser regions collapsed more rapidly than the regions not as dense. As this occurred, the cloud divided into a bunch of dense molecular cloud cores embedded within the large cloud. The molecular cloud collapsed until the center of the core began falling inward faster than the rest of the cloud can follow. The cloud continued to collapse more rapidly from the inside out with the falling material feeding an accretion disk. A protostar was grown in the center. It continued to collapse. The protostars wind and bipolar jets help disperse the remainder of the cloud core to reveal Arcturus and its circumstellar disk. As the protostar collapsed, temperature and pressure increased until hydrogen fusion occurred.
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Nuclear Fusion
Nuclear fusion is an atomic reaction that fuels stars. In nuclear fusion, many nuclei combine together to make a larger one (which is a different element). The result of this is the release of a lot of energy. Stars get their energy through this process, usually converting hydrogen into helium.