What is stellar evolution?

• A. Stellar evolution is the process by which a star changes over the course of time.
• B. Nucleosynthesis is the process by which stars change over the course of time.
• C. Galactic rotation determines the life cycle of a star.
• D. Comets orbit the Sun.

Answer: (A)

Stellar evolution is the process by which a star changes over the course of time. This describes the life story of a star—from its formation in interstellar clouds, through successive fusion-powered stages, to its ultimate fate as a white dwarf, neutron star, or black hole depending on mass. As a star burns hydrogen, then helium and heavier elements, its core composition, energy output, size, and surface temperature shift, driving observable changes in brightness and color over millions to billions of years. Nucleosynthesis—the creation of new atomic nuclei—occurs inside stars and fuels these changes, but the overall idea of stellar evolution is the entire sequence of states a star passes through. The other options don’t fit because galactic rotation concerns how stars orbit within a galaxy, and comets orbit the Sun—topics about galaxies or small bodies, not a single star’s life cycle.