Astronomy
1st Edition
ISBN: 9781938168284
Author: Andrew Fraknoi; David Morrison; Sidney C. Wolff
Publisher: OpenStax
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Textbook Question
Chapter 20, Problem 5E
Describe how the 21-cm line of hydrogen is formed. Why is this line such an important tool for understanding the interstellar medium?
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What evidence can you cite that the interstellar medium contains both gas and dust? (Select all that apply.)
(1)The dust of the interstellar medium can be detected from the emission lines of elements heavier than iron.
(2)The dust of the interstellar medium can be detected by the extinction of light from distant stars.
(3)The dust of the interstellar medium can be detected by the scattering of blue light from distant or embedded objects.
(4)The gas of the interstellar medium can be detected from the radiation of ultraviolet photons.
(5)The gas of the interstellar medium can be detected from the radiation of photons of wavelength 21 cm.
(6)The gas of the interstellar medium can be detected from the absorption lines present in the light from distant stars, which must be caused by a medium of a density and temperature other than that of the stars emitting the light.
Explain why interstellar molecules are best observed at radio wavelengths.
Based on what you know about observations of the interstellar medium at wavelengths other than for visible light, select all of the correct statements from the following list.
-The 21-cm radio observations are of neutral hydrogen.
-Much interstellar dust between stars is not visible.
-The source of hot gas observed at X-ray wavelengths is not known.
-All interstellar material is cool.
-Interstellar dust is observed at ultraviolet wavelengths.
-Giant molecular clouds consist mostly of CO molecules.
-Material observed at wavelengths longer than that of visible light is usually cool.
Chapter 20 Solutions
Astronomy
Ch. 20 - Identify several dark nebulae in photographs in...Ch. 20 - Why do nebulae near hot stars look red? Why do...Ch. 20 - Describe the characteristics of the various kinds...Ch. 20 - Prepare a table listing the different ways in...Ch. 20 - Describe how the 21-cm line of hydrogen is formed....Ch. 20 - Describe the properties of the dust grains found...Ch. 20 - Why is it difficult to determine where cosmic rays...Ch. 20 - What causes reddening of starlight? Explain how...Ch. 20 - Why do molecules, including H2 and more complex...Ch. 20 - Why can’t we use visible light telescopes to study...
Ch. 20 - The mass of the interstellar medium is determined...Ch. 20 - Where does interstellar dust come from? How does...Ch. 20 - Figure 20.2 shows a reddish glow around the star...Ch. 20 - If the red glow around Antares is indeed produced...Ch. 20 - Even though neutral hydrogen is the most abundant...Ch. 20 - The terms H II and H2 are both pronounced “H two.”...Ch. 20 - Suppose someone told you that she had discovered H...Ch. 20 - Describe the spectrum of each of the following: A....Ch. 20 - According to the text, a star must be hotter than...Ch. 20 - From the comments in the text about which kinds of...Ch. 20 - One way to calculate the size and shape of the...Ch. 20 - New stars form in regions where the density of gas...Ch. 20 - Thinking about the topics in this chapter, here is...Ch. 20 - Stars form in the Milky Way at a rate of about 1...Ch. 20 - The 21-cm line can be used not just to find out...Ch. 20 - Astronomers recently detected light emitted by a...Ch. 20 - We can detect 21-cm emission from other galaxies...Ch. 20 - We have said repeatedly that blue light undergoes...Ch. 20 - Suppose that, instead of being inside the Local...Ch. 20 - Suppose that, instead of being inside the Local...Ch. 20 - A molecular cloud is about 1000 times denser than...Ch. 20 - Would you expect to be able to detect an H II...Ch. 20 - Suppose that you gathered a ball of interstellar...Ch. 20 - At the average density of the interstellar medium,...Ch. 20 - Consider a grain of sand that contains 1 mg of...Ch. 20 - H II regions can exist only if there is a nearby...Ch. 20 - In the text, we said that the five-times ionized...Ch. 20 - Dust was originally discovered because the stars...Ch. 20 - How would the density inside a cold cloud (T=10K)...Ch. 20 - The text says that the Local Fluff, which...
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Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, physics and related others by exploring similar questions and additional content below.Similar questions
- How would the density inside a cold cloud (T=10K) compare with the density of the ultra-hot interstellar gas (T=106K) if they were in pressure equilibrium? (It takes a large cloud to be able to shield its interior from heating so that it can be at such a low temperature.) (Hint: In pressure equilibrium, the two regions must have nT equal, where n is the number of particles per unit volume and T is the temperature.) Which region do you think is more suitable for the creation of new stars? Why?arrow_forwardThe mass of the interstellar medium is determined by a balance between sources (which add mass) and sinks (which remove it). Make a table listing the major sources and sinks, and briefly explain each one.arrow_forwardA molecular cloud is about 1000 times denser than the average of the interstellar medium. Let’s compare this difference in densities to something more familiar. Air has a density of about 1 kg/m3, so something 1000 times denser than air would have a density of about 1000 kg/m3. How does this compare to the typical density of water? Of granite? (You can find figures for these densities on the internet.) Is the density difference between a molecular cloud and the interstellar medium larger or smaller than the density difference between air and water or granite?arrow_forward
- Consider a grain of sand that contains 1 mg of oxygen (a typical amount for a medium-sized sand grain, since sand is mostly SiO2). How many oxygen atoms does the grain contain? What is the radius of the sphere you would have to spread them out over if you wanted them to have the same density as the interstellar medium, about 1 atom per cm3? You can look up the mass of an oxygen atom.arrow_forwardPrepare a table listing the different ways in which dust and gas can be detected in interstellar space.arrow_forwardWhere does interstellar dust come from? How does it form?arrow_forward
- Why evidence can you cite that the interstellar medium contains both gas and dust?arrow_forwardDescribe the characteristics of the various kinds of interstellar gas (HII regions, neutral hydrogen clouds, ultra-hot gas clouds, and molecular clouds).arrow_forwardHow are giant molecular clouds (GMCs), the loci of most star formation, themselves formed out of diffuse interstellar gas? What processes determine the distribution of physical conditions within star-forming regions, and why does star formation occur in only a small fraction of the available gas? How is the rate at which stars form determined by the properties of the natal GMC or, on a larger scale, of the interstellar medium (ISM) in a galaxy? What determines the mass distribution of forming stars, the initial mass function (IMF)? Most stars form in clusters (Lada & Lada 2003); how do stars form in such a dense environment and in the presence of enormous radiative and mechanical feedback from other YSOs?arrow_forward
- Absorption lines produced when starlight travels through the interstellar medium indicate that some components of the interstellar medium are cold and of a very low density because a. the lines are blueshifted. b. the lines are redshifted. c. the lines are extremely broad. d. the lines are extremely narrow. e. the lines are much darker than the stellar lines.arrow_forwardAbsorption lines produced by interstellar gas a. are wider than the lines from stars because the gas is hotter than most stars. b. are more narrow than the lines from stars because the gas has a lower pressure than stars. c. indicate that the interstellar medium contains dust. d. indicate that the interstellar medium is expanding away from the sun. e. indicate nothing; none of the above statements are true.arrow_forward1. If a star has a surface temperature of 3000 K but a luminosity 150 times greater than our Sun, what size is this star? Give your answer in units of the solar radius. 2. At what wavelengths do stars of surface temperates 20 000 K, 10 000 K, and 3000 K have their peak intensity? 3. If the Hα absorption line in the spectrum of a galaxy is observed at a wavelength of 6715 ˚A, at what speed is the galaxy moving away from us?arrow_forward
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