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Chapter 15: Problem 16

The interstellar medium is approximately 99 percent gas and percent dust. Why does dust and not gas block a visible-light view of the galactic center?

Short Answer

Expert verified
Dust blocks visible-light views of the galactic center because it scatters and absorbs light efficiently, unlike gas.

Step by step solution

01

Composition of Interstellar Medium

Analyze the composition of the interstellar medium, which consists of approximately 99% gas and about 1% dust.
02

Light Interaction with Gas

Understand that gas primarily consists of individual atoms and molecules that are relatively transparent to visible light. This means gas does not significantly block or scatter visible light.
03

Light Interaction with Dust

Recognize that dust particles, although only 1% of the interstellar medium, are much larger than individual atoms and molecules. They are comparable in size to the wavelength of visible light, causing them to scatter and absorb light efficiently.
04

Scattering and Absorption

Understand how dust scatters and absorbs light. Dust particles block visible light through a combination of absorption and scattering, which diminishes the light’s intensity and makes regions containing dust appear dark to us.
05

Conclusion

Conclude that despite being only a small fraction of the interstellar medium, dust particles block visible-light views of the galactic center because they are effective at scattering and absorbing light.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Galactic Center
The galactic center is the rotational center of a galaxy. In our Milky Way, it is home to a supermassive black hole called Sagittarius A*. Despite its significance, the galactic center is very difficult to observe with visible light.
This is because the dense interstellar medium in that region blocks much of the visible light coming from it. Therefore, astronomers often use other wavelengths, like radio or infrared, which can pass through the interstellar material more easily.
Light Scattering
Light scattering happens when particles in the interstellar medium deflect light in different directions. Dust particles in space are particularly good at this because their sizes are comparable to the wavelength of visible light. When light encounters these particles, it changes direction, causing the light to scatter.
This scattering not only reduces the amount of light that reaches us but also blurs the image of the light source, making it harder to get a clear view of the galactic center.
Light Absorption
Light absorption refers to the process by which matter takes in light energy and converts it to other forms of energy, like heat. Dust particles in the interstellar medium are very good at absorbing visible light. When light hits these dust particles, a significant portion of it is absorbed, preventing it from continuing its journey.
This absorption diminishes the brightness of objects behind the dust and is another reason we can't see the galactic center clearly with visible light.
Dust Particles
Dust particles play a critical role in the interstellar medium. Although they only make up about 1% of it, they have a huge impact on how light travels through space. These particles are bigger than gas molecules but smaller than grains of sand, making them efficient at scattering and absorbing light.
Dust particles block our view of objects in space because they interact with visible light in these specific ways, causing areas with large amounts of dust to appear darker. This is why dust, even though it's a small part of the interstellar medium, can significantly hinder our view of the galactic center.

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Most popular questions from this chapter

The star-forming region 30 Doradus is 160,000 light-years away in the nearby galaxy called the Large Magellanic Cloud and appears about one-sixth as bright as the faintest stars visible to the naked eye. If it were located at the distance of the Orion Nebula (1,300 light-years away), how much brighter than the faintest visible stars would it appear?

Some parts of the Orion Nebula have a blackbody peak wavelength of \(0.29 \mu \mathrm{m} .\) What is the temperature of these parts of the nebula?

Cold neutral hydrogen can be detected because a. it emits light when electrons drop through energy levels. b. it blocks the light from more distant stars. c. it is always hot enough to glow in the radio and infrared wavelengths. d. the atoms in the gas change spin states.

How does the material in interstellar clouds and intercloud gas differ in density and distribution?

Phases of the interstellar medium include (choose all that apply a. hot, low-density gas. b. cold, high-density gas. c. hot, high-density gas. d. cold, low-density gas.
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