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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]
A-type star In the Harvard spectral classification system, a class of main-sequence star having spectra dominated by Balmer absorption lines of hydrogen. Stars of spectral class A are typically blue-white or white in color, measure between 1.4 and 2.1 times the mass of the Sun, and have surface temperatures of 7,600–10,000 kelvin.
Young stellar object (YSO) denotes a star in its early stage of evolution. This class consists of two groups of objects: protostars and pre-main-sequence stars . Classification by spectral energy distribution
The Bubble Nebula (NGC 7635), imaged by the Hubble Space Telescope, is seven light years across. A stellar-wind bubble is a cavity light-years across filled with hot gas blown into the interstellar medium by the high-velocity (several thousand km/s) stellar wind from a single massive star of type O or B.
In roughly 5 billion years, the Sun will cool and expand outward to many times its current diameter (becoming a red giant), before casting off its outer layers as a planetary nebula and leaving behind a stellar remnant known as a white dwarf. In the distant future, the gravity of passing stars will gradually reduce the Sun's retinue of planets.
SN 1054 remnant (Crab Nebula).. A supernova remnant (SNR) is the structure resulting from the explosion of a star in a supernova.The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar material it sweeps up and shocks along the way.
The defining criterion of a shock wave is that the bulk velocity of the plasma drops from "supersonic" to "subsonic", where the speed of sound c s is defined by = / where is the ratio of specific heats, is the pressure, and is the density of the plasma.
The Carina Nebula is an example of a diffuse nebula Most nebulae can be described as diffuse nebulae, which means that they are extended and contain no well-defined boundaries. [ 24 ] Diffuse nebulae can be divided into emission nebulae , reflection nebulae and dark nebulae .