
Concept explainers
To compare:
The chemical composition of the present-day Sun’s core with its composition when the sun was formed.

Answer to Problem 1Q
Presently, the sun’s core has more Helium and less Hydrogen than when the sun was formed.
The change was brought about by Hydrogen fusion.
Explanation of Solution
Introduction All main-sequence stars convert Hydrogen into Helium by thermonuclear reactions. Sun’s main-sequence stage starts with the beginning of the Hydrogen fusion and ends when all Hydrogens in the core get converted to Helium. The Sun started Hydrogen fusion 4.56 billion years ago and it is less than halfway of its main-sequence lifetime.
The Sun’s primary constituent is Hydrogen. At the center of the Sun, thermonuclear fusion occurs under extremely high temperatures. Four Hydrogen nuclei convert to a Helium nucleus. This is a stepwise process and it is known as a proton-proton chain reaction. This process releases a large amount of energy as heat and light. In 4.56 billion years, the amount of Helium in the Sun’s core has increased and the amount of Hydrogen has decreased.
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Chapter 19 Solutions
Universe: Stars And Galaxies
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