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In 1926, in his book The Internal Constitution of the Stars he explained the physics of how stars fit on the diagram. [15] The paper anticipated the later discovery of nuclear fusion and correctly proposed that the star's source of power was the combination of hydrogen into helium, liberating enormous energy.
The Solar System formed at about 9.2 billion years (4.6 Gya), [5]: 22.2.3 with the earliest evidence of life on Earth emerging by about 10 billion years (3.8 Gya). The thinning of matter over time reduces the ability of the matter to gravitationally decelerate the expansion of the universe; in contrast, dark energy is a constant factor tending ...
Schematic of stellar evolution. Stellar evolution starts with the gravitational collapse of a giant molecular cloud. Typical giant molecular clouds are roughly 100 light-years (9.5 × 10 14 km) across and contain up to 6,000,000 solar masses (1.2 × 10 37 kg). As it collapses, a giant molecular cloud breaks into smaller and smaller pieces.
[2] [3] The discovery (by chance in 1965) of the cosmic background radiation suggests that the early universe was dominated by a radiation field, a field of extremely high temperature and pressure. [4] There is background radiation observed across all wavelength regimes, peaking in microwave, but also notable in infrared and X-ray regimes.
As evolutionary models of stars were developed during the 1930s, it was shown that, for stars with the same composition, the star's mass determines its luminosity and radius. Conversely, when a star's chemical composition and its position on the main sequence are known, the star's mass and radius can be deduced.
Evolution is the change in the heritable characteristics of biological populations over successive generations. [1] [2] It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certain characteristics becoming more or less common within a population over successive generations. [3]
The horizontal branch (HB) is a stage of stellar evolution that immediately follows the red-giant branch in stars whose masses are similar to the Sun's. Horizontal-branch stars are powered by helium fusion in the core (via the triple-alpha process) and by hydrogen fusion (via the CNO cycle) in a shell surrounding the core.
The history of scientific thought about the formation and evolution of the Solar System began with the Copernican Revolution. The first recorded use of the term " Solar System " dates from 1704. [ 1 ] [ 2 ] Since the seventeenth century, philosophers and scientists have been forming hypotheses concerning the origins of the Solar System and the ...