Multiple choice

Why do variable stars pulsate in brightness?

  1. Gain in mass

  2. Expansion & contraction of the outer layers

  3. Constant contraction

  4. Movement at a fixed rate
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B Correct answer
Explanation

Variable stars, such as Cepheid variables, pulsate because of the periodic expansion and contraction of their outer layers, which is driven by changes in opacity and temperature.

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