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A star is a luminous spheroid of plasma held together by self-gravity. [1] ... and radii in solar units, based on the characteristics of the Sun. In 2015, ...
A simple chart for classifying the main star types using Harvard classification. In astronomy, stellar classification is the classification of stars based on their spectral characteristics.
A characteristic of population II stars is that despite their lower overall metallicity, they often have a higher ratio of alpha elements (elements produced by the alpha process, like oxygen and neon) relative to iron (Fe) as compared with population I stars; current theory suggests that this is the result of type II supernovas being more ...
Russell's early (1913) versions of the diagram included Maury's giant stars identified by Hertzsprung, those nearby stars with parallaxes measured at the time, stars from the Hyades (a nearby open cluster), and several moving groups, for which the moving cluster method could be used to derive distances and thereby obtain absolute magnitudes for ...
These stars will eventually end their lives as white dwarfs. [59] [60] The most massive stars do not become red giants; instead, their cores quickly become hot enough to fuse helium and eventually heavier elements and they are known as supergiants. They follow approximately horizontal evolutionary tracks from the main sequence across the top of ...
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 ...
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 ...
Almost all elements heavier than hydrogen and helium were created inside the cores of stars. [100] The characteristics of the resulting star depend primarily upon its starting mass. The more massive the star, the greater its luminosity, and the more rapidly it fuses its hydrogen fuel into helium in its core.