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Chapter 19: Problem 8

Explain how it is possible for the core of a red giant to contract at the same time that its outer layers expand.

Short Answer

Expert verified
The core of a red giant contracts because it has run out of hydrogen fuel, and without the energy generation to counteract gravity, it starts to contract. However, the increased temperature and pressure in the core allows for hydrogen in a shell around the core to begin nuclear fusion, generating more heat and causing the outer layers to expand.

Step by step solution

01

Understanding Red Giants

Red giants are stars that have exhausted the hydrogen in their cores and have begun to burn helium. They are in the late stages of stellar evolution and are characterized by their large size and red color.
02

Discussing Core Contraction

When a star has exhausted the hydrogen in its core, nuclear reactions cease. Without the energy generation to counteract the inward pull of gravity, the core starts to contract. This contraction increases the temperature and pressure in the core.
03

Explaining Outer Layers Expansion

Meanwhile, the increased temperature and pressure in the core allows for hydrogen in a shell around the core to begin nuclear fusion, generating more heat. This causes the outer layers of the star to expand. Furthermore, as the core contracts, the outer layers are less gravitationally bound and puff out even more.

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Most popular questions from this chapter

Why do Cepheid stars pulsate? Why are these stars important to astronomers who study galaxies beyond the Milky Way?

As a red giant, the Sun's luminosity will be about 2000 times greater than it is now, so the amount of solar energy falling on the Earth will increase to 2000 times its present-day value. Hence, to maintain thermal equilibrium, each square meter of the Earth's surface will have to radiate 2000 times as much energy into space as it does now. Use the Stefan-Boltzmann law to determine what the Earth's surface temperature will be under these conditions. (Hint: The present-day Earth has an average surface temperature of \(14^{\circ} \mathrm{C}\).)

Why do astronomers attribute the observed Doppler shifts of a Cepheid variable to pulsation, rather than to some other cause, such as orbital motion?

Explain why the majority of the stars visible through telescopes are main- sequence stars.

What is a Roche lobe? What is the inner Lagrangian point? Why are Roche lobes important in close binary star systems?
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