Definition
Stars are spheres of plasma in hydrostatic equilibrium, where the inward force of gravity is balanced by the outward gas pressure. The energy source for the gas is gravitation, sustained and prolonged by nuclear energy resulting from thermonuclear fusion reactions in the hot stellar interior. Stars form by contraction of a portion of a molecular cloud.
Overview
Stars are spheres of gas that can most of the time be considered as in hydrostatic and radiative equilibrium. They form during the contraction of cold molecular clouds. In the process of star formation, a part of the original matter of the cloud may form a disk around the star, and in such a disk, planets could be built.
At the center of the collapsing cloud, the temperature rises until it is sufficient for nuclear reactions to take place; thus, a new star is born. Through these reactions, new chemical elements are synthesized (➔ nucleosynthesis) accompanied by a production of energy. The energy release sustains the...
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Eggenberger, P., Ekström, S. (2023). Stars. In: Gargaud, M., et al. Encyclopedia of Astrobiology. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-662-65093-6_1503
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DOI: https://doi.org/10.1007/978-3-662-65093-6_1503
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Publisher Name: Springer, Berlin, Heidelberg
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