2025 ASTR 1102 Final Exam with accurate questions

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2025 ASTR 1102 Final Exam with accurate questions and verified answers covering stellar evolution, galaxies, cosmology, and advanced astronomy concepts.

An A5 star has 5x the mass of the Sun, but 15x the luminosity.How long will it live?

• 1/3rd of the Sun's lifetime
• 1/5th of the Sun's lifetime
• 3 times the Sun's lifetime - ANSWER-A

Why is the sun gradually and very slowly get's brighter during its lifetime in the main-sequence?

• Because newly made helium in the core of the sun produces

more nuclear energy via fusion during the main-sequence.

• Because as hydrogen converts to helium in the core, the

pressure slowly decreases and gravity slowly compresses the core making it hotter therefore producing more luminosity.

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• Because it continues to burn hydrogen in a thin shell around

the core. - ANSWER-B

Which of the following reaction rates is more sensitive to temperature?

• The CNO cycle
• The 3α process
• The proton-proton (pp) chain - ANSWER-B

Which of the following reaction pairs burn hydrogen to helium?

• The CNO cycle and the 3α process
• The 3α process and the pp chain
• The proton-proton (pp) chain and the CNO cycle -

ANSWER-C

How do red giant stars generate energy?

• Fusion of hydrogen in their core
• Fusion of hydrogen in a shell around their core
• Fusion of helium in their core
• Fusion of helium in a shell around their core
• Fusion of carbon - ANSWER-B 2 / 4

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Why after the 'helium flash' stars become less luminous in the HR diagram?

• Because a hydrogen-burning shell around the core does not

produce as much energy as hydrogen-core burning, therefore luminosity drops.

• Because they have exhausted their main nuclear fuel and no

reactions can produce more luminosity in the core.

• Because hydrogen fusion produces less energy and therefore

the luminosity drops.

• Because the core expands, the temperature drops and

therefore the reaction rates and the luminosity drops so the envelope contracts and heat up. - ANSWER-D

A star is 10 times more massive than the sun and 2000 times more luminous. How many years will it spend in the main-

sequence? Reminder: The sun's main-sequence lifetime is 10

billion years.

• 50 million years 3 / 4

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• 500 million years
• 5 million years - ANSWER-A

Once the star in Part 1 of the Assignment burns the hydrogen in its core and leaves the main sequence, what type of reaction will be taking place in the core involving helium?

• The CNO Cycle
• The pp-chain
• The 3α process - ANSWER-C

What type of nuclear burning is going on in the sun right now?

• CNO cycle
• pp-chain
• Triple-alpha - ANSWER-B

What type of nuclear burning will take place in the hydrogen shell of the sun when it becomes a sub-giant star?

• CNO cycle
• pp-chain
• Triple-alpha - ANSWER-A
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