When a Star First Begins the Long Path Toward Becoming

question 34

Multiple Choice

When a star first begins the long path toward becoming a red giant, a layer of hydrogen around the core begins to undergo fusion. If this layer was too cold to do fusion throughout the main sequence stage, why is it suddenly warm enough?

• A) as the star expands, all the layers heat up
• B) the core is collapsing under its own weight and heating up from the compression; this heats the next layer up
• C) the heat comes from the fusion of carbon in the core, which starts right away
• D) the heat comes from the outer layers of the star, which are much hotter than the core
• E) this is an unsolved problem in astronomy, but something must be heating that layer, since we observe red giants out there

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