hydrogen is the true power source for the sun and other main sequence stars.
hydrogen is the true power source for the sun and other main sequence stars.
what is the true power source for the sun and other main sequence stars?
hydrogen
the main sequence is sometimes divided into upper and lower parts, based on the dominant process that a star uses to generate energy. stars below about 1.5 times the mass of the sun () primarily fuse hydrogen atoms together in a series of stages to form helium, a sequence called the proton–proton chain. above this mass, in the upper main sequence, the nuclear fusion process mainly uses atoms of carbon, nitrogen and oxygen as intermediaries in the cno cycle that produces helium from hydrogen atoms. main-sequence stars with more than two solar masses undergo convection in their core regions, which acts to stir up the newly created helium and maintain the proportion of fuel needed for fusion to occur. below this mass, stars have cores that are entirely radiative with convective zones near the surface. with decreasing stellar mass, the proportion of the star forming a convective envelope steadily increases. main-sequence stars below undergo convection throughout their mass. when core convection does not occur, a helium-rich core develops surrounded by an outer layer of hydrogen.
main sequence
color–color diagrams allow for these effects to be isolated. as the color–color relationships of main sequence stars are well known, a theoretical main sequence can be plotted for reference, as is done with the solid black line in the example to the right. interstellar dust scattering is also well understood, allowing bands to be drawn on a color–color diagram defining the region in which stars reddened by interstellar dust are expected to be observed, indicated on the color–color diagram by dashed lines. the typical axes for infrared color–color diagrams have (h–k) on the horizontal axis and (j–h) on the vertical axis (see infrared astronomy for information on band color designations). on a diagram with these axes, stars which fall to the right of the main sequence and the reddening bands drawn are significantly brighter in the k band than main sequence stars, including main sequence stars which have experienced reddening due to interstellar dust. of the j, h, and k bands, k is the longest wavelength, so objects which are anomalously bright in the k band are said to exhibit infrared excess. these objects are likely protostellar in nature, with the excess radiation at long wavelengths caused by suppression by the reflection nebula in which the protostars are embedded. color–color diagrams can be used then as a means of studying stellar formation, as the state of a star in its formation can be roughly determined by looking at its position on the diagram.
color–color diagram