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In forming the stellar structure equations (exploiting the assumed spherical symmetry), one considers the matter density (), temperature (), total pressure (matter plus radiation) (), luminosity (), and energy generation rate per unit mass () in a spherical shell of a thickness at a distance from the center of the star.
This is required by the stellar equation of state; for a massive star to maintain equilibrium, the outward pressure of radiated energy generated in the core not only must but will rise to match the titanic inward gravitational pressure of its envelope. Thus, the most massive stars may remain on the main sequence for only a few million years ...
Note that the brighter the star, the smaller the magnitude: Bright "first magnitude" stars are "1st-class" stars, while stars barely visible to the naked eye are "sixth magnitude" or "6th-class". The system was a simple delineation of stellar brightness into six distinct groups but made no allowance for the variations in brightness within a group.
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.
The spectral type is not a numerical quantity, but the sequence of spectral types is a monotonic series that reflects the stellar surface temperature. Modern observational versions of the chart replace spectral type by a color index (in diagrams made in the middle of the 20th Century, most often the B-V color) of the stars.
The [α/Fe] versus [Fe/H] diagram is a type of graph commonly used in stellar and galactic astrophysics. It shows the logarithmic ratio number densities of diagnostic elements in stellar atmospheres compared to the solar value. The x-axis represents the abundance of iron (Fe) vs. hydrogen (H), that is, [Fe/H].
For simplicity, the stellar structure equations are written without explicit time dependence, with the exception of the luminosity gradient equation: = Here L is the luminosity, ε is the nuclear energy generation rate per unit mass and ε ν is the luminosity due to neutrino emission (see below for the other quantities). The slow evolution of ...
1 Age (stellar) 2 Astrometry parameters. 3 Cosmological parameters. 4 Distance description. 5 Galaxy comparison. 6 Luminosity comparison. 7 Mass comparison. 8 ...