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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
Star formation theory, as well as accounting for the formation of a single star, must also account for the statistics of binary stars and the initial mass function. Most stars do not form in isolation but as part of a group of stars referred as star clusters or stellar associations. [2]
Swimming animals that are denser than water must generate lift or adapt a benthic lifestyle. Movement of the fish to generate hydrodynamic lift is necessary to prevent sinking. Often, their bodies act as hydrofoils, a task that is more effective in flat-bodied fish. At a small tilt angle, the lift is greater for flat fish than it is for fish ...
It also does not explain how star formation ceases in galaxies. Theories of galaxy evolution must therefore be able to explain how star formation turns off in galaxies. This phenomenon is called galaxy "quenching". [16] Stars form out of cold gas (see also the Kennicutt–Schmidt law), so a galaxy is quenched when it has no more cold gas ...
External sources of energy may have triggered these reactions, including lightning, radiation, atmospheric entries of micro-meteorites, and implosion of bubbles in sea and ocean waves. More recent research has found amino acids in meteorites, comets, asteroids, and star-forming regions of space.
The treacherous waves of the North Sea have become an unlikely TikTok sensation. The North Sea — a body of water located between Great ritain, Denmark, the Netherlands, Norway, Germany, Belgium ...
This birth of a new star occurs approximately 100,000 years after the collapse begins. [8] Objects at this stage are known as Class I protostars, which are also called young T Tauri stars, evolved protostars, or young stellar objects. By this time, the forming star has already accreted much of its mass; the total mass of the disk and remaining ...
The central stars of planetary nebulae are very hot. Their luminosity, though, is very low, implying that they must be very small. A star can collapse to such a small size only once it has exhausted all its nuclear fuel, so planetary nebulae came to be understood as a final stage of stellar evolution.