By Jagjit Singh
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Extra info for Great Ideas and Theories of Modern Cosmology
But in both stages of its life, namely as a contracting globule of gas and as a mainsequence star, the more massive the star, the briefer its life span. Thus a star of one solar mass has sufficient store of hydrogen to enable it to shine in a steady state for ten billion years, while stars with a significantly larger stock of hydrogen have much shorter lives. The reason is that a more massive star squanders its talents - hydrogen - like a true prodigal. A star ten times as massive as the sun, for example, will squander its hydrogen a thousandfold faster.
3,000°K . We shall now take up the question of chemical composition. The earlier cosmologists believed that stellar m aterial, or at least its inner core, consisted of heavier materials like iron and silicon. But the assumption did not agree with theory. W hat theory ? This leads us to a slight digression on the theory of stellar structure. When we look upon a large mass such as, say, the mass of water in the Pacific Ocean, we generally do not realize to what terrific pressure its lower depths must be subject - unless we hap pen to be in a submerged submarine.
Their difference (B — V) is called the colour index of the star. The difference U —£, the so-called ultra-violet excess, is also computed. It is a measure of the difference in a star’s radia tion at short wavelengths vis-à-vis its radiation at longer but neighbouring wavelengths. We next come to the fourth attribute, namely the spectral class of a star. When we pass light from a star through a glass prism or grating, it is decomposed into its composite colours just as sun light is broken up into rainbow colours when viewed through a prism.