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Blue giant is not a strictly defined term and it is applied to a wide variety of different types of stars. They have in common a moderate increase in size and luminosity compared to main-sequence stars of the same mass or temperature, and are hot enough to be called blue, meaning spectral class O, B, and sometimes early A.
A blue supergiant (BSG) is a hot, luminous star, often referred to as an OB supergiant. They are usually considered to be those with luminosity class I and spectral class B9 or earlier, [ 1 ] although sometimes A-class supergiants are also deemed blue supergiants.
If that were true, then stars would start their lives as very hot "early-type" stars and then gradually cool down into "late-type" stars. This mechanism provided ages of the Sun that were much smaller than what is observed in the geologic record , and was rendered obsolete by the discovery that stars are powered by nuclear fusion . [ 71 ]
Blue hypergiants that do not show LBV characteristics may be progenitors of LBVs, or vice versa, or both. [17] Lower mass LBVs may be a transitional stage to or from cool hypergiants or are different type of object. [17] [18] Wolf–Rayet stars are extremely hot stars that have lost much or all of their outer layers. WNL is a term used for late ...
A B-type main-sequence star (B V) is a main-sequence (hydrogen-burning) star of spectral type B and luminosity class V. These stars have from 2 to 16 times the mass of the Sun and surface temperatures between 10,000 and 30,000 K. [1] B-type stars are extremely luminous and blue.
Hot subdwarfs, of bluish spectral types O and B are an entirely different class of object than cool subdwarfs; they are also called "extreme horizontal-branch stars". Hot subdwarf stars represent a late stage in the evolution of some stars, caused when a red giant star loses its outer hydrogen layers before the core begins to fuse helium.
For the hottest stars the difference is not directly observable and for these stars, the terms "dwarf" and "giant" refer to differences in spectral lines which indicate whether a star is on or off the main sequence. Nevertheless, very hot main-sequence stars are still sometimes called dwarfs, even though they have roughly the same size and ...
Such stars predominate within clusters because hotter and more massive stars have exploded as supernovae, or evolved through planetary nebula phases to end as white dwarfs. Yet a few rare blue stars exist in globulars, thought to be formed by stellar mergers in their dense inner regions; these stars are known as blue stragglers.