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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鈥檚 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 Sun took 30 million years to evolve from a collapsing cloud core to a star, with 10 million of those years spent on its Hayashi track. It will spend a total of 10 billion years on the main sequence. Suppose the Sun's main- sequence lifetime were compressed into a single day. a. How long would the total collapse phase last? b. How long would the Sun spend on its Hayashi track?

Neutral hydrogen emits radiation at a radio wavelength of \(21 \mathrm{cm}\) when an atom drops from a higher-energy spin state to a lower-energy spin state. On average, each atom remains in the higher energy state for 11 million years \(\left(3.5 \times 10^{14}\) seconds) \right. a. What is the probability that any given atom will make the transition in 1 second? b. If there are \(6 \times 10^{59}\) atoms of neutral hydrogen in a \(500-M_{\text {sun }}\) cloud, how many photons of 21 -cm radiation will the cloud emit each second? c. How does this number compare with the \(1.8 \times 10^{45}\) photons emitted each second by a solar-type star?

Astronomers determined the composition of the interstellar medium from a. observing its emission and absorption lines. b. measuring the composition of the planets. c. return samples from spacecraft. d. composition of meteorites.

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a 2.5 -meter telescope on a modified Boeing 747 aircraft. Go to the SOFIA website (http://sofia.usra.edu). Why have astronomers put an infrared telescope on an airplane? What has been detected with this telescope?

Interstellar gas atoms typically cool by colliding with other gas atoms or grains of dust; during the collision, each gas atom loses energy and hence its temperature is lowered. How does this explain why very low-density gases are generally so hot, while dense gases tend to be so cold?
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