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Chapter 18: Problem 10

The interior of a dark nebula is billions of times less dense than the air that you breathe. How, then, are dark nebulae able to block out starlight?

Short Answer

Expert verified
Dark nebulae are capable of blocking out starlight because, despite their low density, they are composed of dust and gas that absorb, refract, and scatter the light over vast distances. Therefore, the starlight doesn't make it through the dark nebula, making it appear dark against the brighter backdrop.

Step by step solution

01

Nature of Dark Nebulae

A dark nebula isn't just empty space with little matter in it. As with other types of nebulae, it is filled with interstellar dust and gas. Despite the fact that they are 'less dense', their size and composition play key roles in their interaction with light.
02

Composition and Size

Dark nebulae are very large, many light years across, and let's not forget; they are filled with dust. This dust, though not dense as per earthly standards, extends across huge distances and is the main factor that makes dark nebulae opaque. The dust particles absorb light from the stars making dark nebulae block out starlight.
03

Absorption of Starlight

Starlight, when it encounters the dust within a dark nebula, is absorbed, refracted, and scattered. This means that it is either consumed and turned into heat, bent away from its original line of travel, or diffused in every direction. All these actions end up blocking or significantly reducing the amount of light that makes it through the nebula, making it appear dark against the backdrop of brighter stars and nebulae.

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Most popular questions from this chapter

Why are low temperatures necessary in order for protostars to form inside dark nebulae?

What are stationary absorption lines? In what sort of spectra are they seen? How do they give evidence for the existence of the interstellar medium?

In recent years astronomers have been able to learn about the character of the interstellar medium in the vicinity of the Sun. Search the World Wide Web for information about aspects of the nearby interstellar medium, including features called the Local Interstellar Cloud and the Local Bubble. How do astronomers study the nearby interstellar medium? What makes these studies difficult? Is the interstellar medium relatively uniform in our neighborhood, or is it clumpy? If the latter, is our solar system in a relatively thin or thick part of the interstellar medium? How is our solar system moving through the interstellar medium?

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What are H II regions? Near what kinds of stars are they found? Why do only these stars give rise to H II regions?
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