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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 ...
During a star's evolution, convective mixing episodes moves material, within which the CNO cycle has operated, from the star's interior to the surface, altering the observed composition of the star. Red giant stars are observed to have lower carbon-12/carbon-13 and carbon-12/nitrogen-14 ratios than do main sequence stars, which is considered to ...
Energy Star (trademarked ENERGY STAR) is an energy-efficiency program administered by the U.S. Environmental Protection Agency (EPA) in partnership with the U.S. Department of Energy (DOE). [ 2 ] [ 3 ] [ 4 ] The EPA establishes energy efficiency specifications, and those that meet these specifications are eligible to display the ENERGY STAR logo.
In higher-mass stars, the dominant energy production process is the CNO cycle, which is a catalytic cycle that uses nuclei of carbon, nitrogen and oxygen as intermediaries and in the end produces a helium nucleus as with the proton–proton chain. [22] During a complete CNO cycle, 25.0 MeV of energy is released.
This process yields 4.48 eV of energy distributed over the rotational and vibrational modes, kinetic energy of the H 2 molecule, as well as heating the dust grain. This kinetic energy, as well as the energy transferred from de-excitation of the hydrogen molecule through collisions, heats the gas.
The stages of the process are well defined in stars with masses around 1 M ☉ or less. In high mass stars, the length of the star formation process is comparable to the other timescales of their evolution, much shorter, and the process is not so well defined. The later evolution of stars is studied in stellar evolution.
An illustration of the structure of the Sun and a red giant star, showing their convective zones. These are the granular zones in the outer layers of these stars. The convection zone of a star is the range of radii in which energy is transported outward from the core region primarily by convection rather than radiation.
The process is sometimes known as "hot dry rock" (HDR). [134] Unlike conventional geothermal energy extraction, EGS may be feasible anywhere in the world, depending on the cost of drilling. [135] EGS projects have so far primarily been limited to demonstration plants, as the technology is capital-intensive due to the high cost of drilling. [136]