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Representative lifetimes of stars as a function of their masses The change in size with time of a Sun-like star Artist'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 right Chart of stellar evolution A mass-radius plot ...
It also does not explain how star formation ceases in galaxies. Theories of galaxy evolution must therefore be able to explain how star formation turns off in galaxies. This phenomenon is called galaxy "quenching". [16] Stars form out of cold gas (see also the Kennicutt–Schmidt law), so a galaxy is quenched when it has no more cold gas ...
Hoyle concluded that iron must have formed within giant stars. [39] From this, in 1945 and 1946, Hoyle constructed the final stages of a star's life cycle. As the star dies, it collapses under its weight, leading to a stratified chain of fusion reactions: carbon-12 fuses with helium to form oxygen-16, oxygen-16 fuses with helium to produce neon ...
Red giants form when stars have exhausted their supply of hydrogen for nuclear fusion and begin to die. In about 5 or 6 billion years, our sun will become a red giant, puffing up and expanding as ...
Stars evolve because of changes in their composition (the abundance of their constituent elements) over their lifespans, first by burning hydrogen (main sequence star), then helium (horizontal branch star), and progressively burning higher elements. However, this does not by itself significantly alter the abundances of elements in the universe ...
As stars evolve, so do their emissions; younger stars tend to be the most active, meaning they have stronger winds, larger flaring events, and an increased frequency of CMEs. [13] This means that planets orbiting younger stars would endure more volatile stellar events that impact their habitable and abiogenesis zones, perhaps even making them ...
An interstellar cloud of gas will remain in hydrostatic equilibrium as long as the kinetic energy of the gas pressure is in balance with the potential energy of the internal gravitational force. Mathematically this is expressed using the virial theorem , which states that to maintain equilibrium, the gravitational potential energy must equal ...
Typical boundary conditions set the values of the observable parameters appropriately at the surface (=) and center (=) of the star: () =, meaning the pressure at the surface of the star is zero; () =, there is no mass inside the center of the star, as required if the mass density remains finite; () =, the total mass of the star is the star's ...