Representative lifetimes of stars as a function of their massesThe change in size with time of a Sun-like starArtist's depiction of the life cycle of a Sun-like star, starting as a main-sequence star at lower left then expanding through the subgiant and giant phases, until its outer envelope is expelled to form a planetary nebula at upper rightChart of stellar evolution
Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is considerably longer than the current age of the universe. The table shows the lifetimes of stars as a function of their masses.[1] All stars are formed from collapsing clouds of gas and dust, often called nebulae or molecular clouds. Over the course of millions of years, these protostars settle down into a state of equilibrium, becoming what is known as a main-sequence star.
Nuclear fusion powers a star for most of its existence. Initially the energy is generated by the fusion of hydrogen atoms at the core of the main-sequence star. Later, as the preponderance of atoms at the core becomes helium, stars like the Sun begin to fuse hydrogen along a spherical shell surrounding the core. This process causes the star to gradually grow in size, passing through the subgiant stage until it reaches the red-giant phase. Stars with at least half the mass of the Sun can also begin to generate energy through the fusion of helium at their core, whereas more-massive stars can fuse heavier elements along a series of concentric shells. Once a star like the Sun has exhausted its nuclear fuel, its core collapses into a dense white dwarf and the outer layers are expelled as a planetary nebula. Stars with around ten or more times the mass of the Sun can explode in a supernova as their inert iron cores collapse into an extremely dense neutron star or black hole. Although the universe is not old enough for any of the smallest red dwarfs to have reached the end of their existence, stellar models suggest they will slowly become brighter and hotter before running out of hydrogen fuel and becoming low-mass white dwarfs.[2]
Stellar evolution is not studied by observing the life of a single star, as most stellar changes occur too slowly to be detected, even over many centuries. Instead, astrophysicists come to understand how stars evolve by observing numerous stars at various points in their lifetime, and by simulating stellar structure using computer models.
^Bertulani, Carlos A. (2013). Nuclei in the Cosmos. World Scientific. ISBN 978-981-4417-66-2.
^Laughlin, Gregory; Bodenheimer, Peter; Adams, Fred C. (1997). "The End of the Main Sequence". The Astrophysical Journal. 482 (1): 420–432. Bibcode:1997ApJ...482..420L. doi:10.1086/304125.
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often the endpoints of stellarevolution and, in this respect, are also called stellar remnants. The state and type of a stellar remnant depends primarily...
In astrophysics, stellar nucleosynthesis is the creation of chemical elements by nuclear fusion reactions within stars. Stellar nucleosynthesis has occurred...
21–25. ISBN 978-1466584617. Bisnovatyi-Kogan, G. S. (2013). Stellar Physics: StellarEvolution and Stability. Translated by Blinov, A. Y.; Romanova, M. Springer...
Stellar structure models describe the internal structure of a star in detail and make predictions about the luminosity, the color and the future evolution...
Salaris, Maurizio; Cassisi, Santi (2005). "Evolution of Stars and Stellar Populations". Evolution of Stars and Stellar Populations: 400. Bibcode:2005essp.book...
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parent molecular cloud. It is the earliest phase in the process of stellarevolution. For a low-mass star (i.e. that of the Sun or lower), it lasts about...
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stars of less than 3 M☉ in the pre-main-sequence phase (PMS phase) of stellarevolution. It is named after Japanese astrophysicist Chushiro Hayashi. On the...
Retrieved 24 February 2009. Arizona State University (1 June 2020). "Class of stellar explosions found to be galactic producers of lithium". EurekAlert!. Retrieved...
few tens of millennia, compared to considerably longer phases of stellarevolution. Once all of the red giant's atmosphere has been dissipated, energetic...
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mass to fuse hydrogen and helium, hence do not undergo the usual stellarevolution that limits the lifetime of stars. A substellar object with a mass...
diagram populated by evolved cool luminous stars. This is a period of stellarevolution undertaken by all low- to intermediate-mass stars (about 0.5 to 8...
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the high temperature of the corona. Stellar winds from main-sequence stars do not strongly influence the evolution of lower-mass stars such as the Sun...
formed within outflowing and cooling gases from earlier presolar stars. The stellar nucleosynthesis that took place within each presolar star gives to each...
around young stellar objects Circumstellar dust Common envelopes Stellarevolution Leao; Patrick De Laverny; Mekarnia; De Medeiros; Benoit Vandame (2007)...
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