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Chapter 20: Problem 11

What is a white dwarf? Does it produce light in the same way as a star like the Sun?

Short Answer

Expert verified
A white dwarf is a dense, dim star, about the size of Earth but with a mass similar to the Sun. It shines because it is hot and radiates energy away as light, not because of ongoing nuclear fusion like in a star like the Sun. As it cools over billions of years, its light will fade.

Step by step solution

01

Define White Dwarf

A white dwarf is a type of star that is very dense and not very bright compared to other stars. It's a compact stellar object composed mostly of electron-degenerate matter. A white dwarf is approximately the size of the Earth but has the mass close to that of the Sun.
02

Explain the source of a White Dwarf’s Light

Unlike normal stars, white dwarfs no longer undergo nuclear fusion, rather, they shine because they are hot and radiate energy away as light. As they cool down over billions of years, they will fade until they no longer emit significant amounts of light, becoming a black dwarf.
03

Compare to the Sun’s Light Production

In contrast, a star like the Sun produces light and heat through nuclear fusion in its core. The Sun fuses hydrogen into helium and in the process, it releases a tremendous amount of energy in the form of light and heat. So, while both white dwarfs and stars like the Sun produce light, the processes through which they do so are different.

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Most popular questions from this chapter

Consider a high-mass star just prior to a supernova explosion, with a core of diameter \(20 \mathrm{~km}\) and density \(4 \times 10^{17}\) \(\mathrm{kg} / \mathrm{m}^{3}\). (a) Calculate the mass of the core. Give your answer in kilograms and in solar masses. (b) Calculate the force of gravity on a 1-kg object at the surface of the core. How many times larger is this than the gravitational force on such an object at the surface of the Earth, which is about 10 newtons? (c) Calculate the escape speed from the surface of the star's core. Give your answer in \(\mathrm{m} / \mathrm{s}\) and as a fraction of the speed of light. What does this tell you about how powerful a supernova explosion must be in order to blow material away from the star's core?

The major final product of silicon fusion is \({ }^{56} \mathrm{Fe}\), an isotope of iron with 26 protons and 30 neutrons. This is also the most common isotope of iron found on Earth. Discuss what this tells you about the origin of the solar system.

Why does the mass of a star play such an important role in determining the star's evolution?

Why do we not observe planetary nebulae that are more than about 50,000 years old?

. On an H-R diagram, sketch the evolutionary track that the Sun will follow from when it leaves the main sequence to when it becomes a white dwarf. Approximately how much mass will the Sun have when it becomes a white dwarf? Where will the rest of the mass go?
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