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By definition, each population group shows the trend where lower metal content indicates higher age of stars. Hence, the first stars in the universe (very low metal content) were deemed population III, old stars (low metallicity) as population II, and recent stars (high metallicity) as population I. [6] The Sun is considered population I, a ...
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
The first generation of stars, known as Population III stars, formed within a few hundred million years after the Big Bang. [57] These stars were the first source of visible light in the universe after recombination. Structures may have begun to emerge from around 150 million years, and early galaxies emerged from around 180 to 700 million years.
The age of the oldest known stars approaches the age of the universe, about 13.8 billion years. Some of these are among the first stars from reionization (the stellar dawn), ending the Dark Ages about 370,000 years after the Big Bang. [1] This list includes stars older than 12 billion years, or about 87% of the age of the universe.
The W51 nebula in Aquila - one of the largest star factories in the Milky Way (August 25, 2020). Star formation is the process by which dense regions within molecular clouds in interstellar space, sometimes referred to as "stellar nurseries" or "star-forming regions", collapse and form stars. [1]
The first one, the proton–proton chain reaction, is the dominant energy source in stars with masses up to about the mass of the Sun. The second process, the carbon–nitrogen–oxygen cycle , which was also considered by Carl Friedrich von Weizsäcker in 1938, is more important in more massive main-sequence stars.
HE 1523-0901 is the first star whose age was determined using the decay of the radioactive elements uranium and thorium in tandem with measurements of several neutron capture elements. [7] It is believed to have formed directly from the remnants of the first-generation stars that reached the end of their longevity and exploded as supernovae ...
In massive stars (greater than about 1.5 M ☉), the core temperature is above about 1.8×10 7 K, so hydrogen-to-helium fusion occurs primarily via the CNO cycle. In the CNO cycle, the energy generation rate scales as the temperature to the 15th power, whereas the rate scales as the temperature to the 4th power in the proton-proton chains. [2]