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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
Stars evolve because of changes in their composition (the abundance of their constituent elements) over their lifespans, first by burning hydrogen (main sequence star), then helium (horizontal branch star), and progressively burning higher elements. However, this does not by itself significantly alter the abundances of elements in the universe ...
In the dense nebulae where stars are produced, much of the hydrogen is in the molecular (H 2) form, so these nebulae are called molecular clouds. [4] The Herschel Space Observatory has revealed that filaments, or elongated dense gas structures, are truly ubiquitous in molecular clouds and central to the star formation process. They fragment ...
As stars evolve, so do their emissions; younger stars tend to be the most active, meaning they have stronger winds, larger flaring events, and an increased frequency of CMEs. [13] This means that planets orbiting younger stars would endure more volatile stellar events that impact their habitable and abiogenesis zones, perhaps even making them ...
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. Over time, this hydrogen fuel is completely converted into helium, and the star begins to evolve. The fusion of helium requires a ...
Objects at this stage are known as Class I protostars, [16] which are also called young T Tauri stars, evolved protostars, or young stellar objects. [16] By this time the forming star has already accreted much of its mass: the total mass of the disk and remaining envelope does not exceed 10–20% of the mass of the central YSO. [37]
The most powerful telescope to be launched into space has made history by detecting a record number of new stars in a distant galaxy. NASA's James Webb Space Telescope, history's largest and most ...
The formation of stars is of particular interest. Research published in 2009 presents spectroscopic observations of so-called "young stellar objects" viewed in the Large Magellanic Cloud with the Spitzer Space Telescope. This research suggests that water, or, more specifically, ice, plays a large role in the formation of these eventual stars [3]