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In astrophysics, stellar nucleosynthesis is the creation of chemical elements by nuclear fusion reactions within stars. Stellar nucleosynthesis has occurred since the original creation of hydrogen, helium and lithium during the Big Bang. As a predictive theory, it yields accurate estimates of the observed abundances of the elements.
Stellar evolution is the process by which a star changes over the course of its lifetime and how it can lead to the creation of a new star. 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 ...
Stellar nucleosynthesis is the nuclear process by which new nuclei are produced. It occurs in stars during stellar evolution. It is responsible for the galactic abundances of elements from carbon to iron.
The interstellar medium consists of 10 4 to 10 6 particles per cm 3, and is typically composed of roughly 70% hydrogen, 28% helium, and 1.5% heavier elements by mass. The trace amounts of heavier elements were and are produced within stars via stellar nucleosynthesis and ejected as the stars pass beyond the end of their main sequence lifetime.
It is the earliest phase in the process of stellar evolution. [1] For a low-mass star (i.e. that of the Sun or lower), it lasts about 500,000 years. [2] The phase begins when a molecular cloud fragment first collapses under the force of self-gravity and an opaque, pressure-supported core forms inside the collapsing fragment.
The early Universe consisted of only the light elements formed during Big Bang nucleosynthesis. Stellar structure and the Hertzsprung–Russell diagram indicate that the length of the lifetime of a star depends greatly on its initial mass, with the most massive stars being very short-lived, and less massive stars are longer-lived.
The s-process is believed to occur mostly in asymptotic giant branch stars, seeded by iron nuclei left by a supernova during a previous generation of stars. In contrast to the r-process which is believed to occur over time scales of seconds in explosive environments, the s-process is believed to occur over time scales of thousands of years, passing decades between neutron captures.
Indeed, none of these primordial isotopes of the elements from beryllium to oxygen have yet been detected, although those of beryllium and boron may be able to be detected in the future. So far, the only stable nuclides known experimentally to have been made during Big Bang nucleosynthesis are protium, deuterium, helium-3, helium-4, and lithium-7.