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Westerhout 51 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]
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 ...
In particular, 24μ infrared (MIPS) emission shows where a new generation of stars heats the remains of the supernova remnant that induced their formation. In contrast to star formation in density-wave theories, which are limited to disk-shaped galaxies and produce global spiral patterns, SSPSF applies equally well to spirals, to irregular ...
Star formation; Object classes; Interstellar medium; Molecular cloud; Bok globule; Dark nebula; Young stellar object; Protostar; Pre-main-sequence star; T Tauri star; Herbig Ae/Be star; Herbig–Haro object; Theoretical concepts; Accretion; Initial mass function; Jeans instability; Kelvin–Helmholtz mechanism; Nebular hypothesis; Planetary ...
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 ]
When a star runs out of hydrogen to fuse in its core, it begins to contract and heat up. If the central temperature rises to 10 8 K, [ 6 ] six times hotter than the Sun's core, alpha particles can fuse fast enough to get past the beryllium-8 barrier and produce significant amounts of stable carbon-12.
Class II objects have circumstellar disks and correspond roughly to classical T Tauri stars, while Class III stars have lost their disks and correspond approximately to weak-line T Tauri stars. An intermediate stage where disks can only be detected at longer wavelengths (e.g., at 24 μ m {\displaystyle 24{\mu }m} ) are known as transition-disk ...
The third dredge-up occurs after a star enters the asymptotic giant branch, after a flash occurs in a helium-burning shell. The third dredge-up brings helium, carbon, and the s-process products to the surface, increasing the abundance of carbon relative to oxygen; in some larger stars this is the process that turns the star into a carbon star. [3]