Universe
11th Edition
ISBN: 9781319039448
Author: Robert Geller, Roger Freedman, William J. Kaufmann
Publisher: W. H. Freeman
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Chapter 18, Problem 36Q
To determine
The reason behind the recent discovery of the giant molecular clouds despite being the largest objects in the galaxy.
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A two-arm spiral density wave is moving through the Galactic
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If you assume that a globular cluster 4 arc minutes in diameter is actually 27 pc in diameter, how far away is it? (Hint: Use the small-angle formula.)
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Chapter 18 Solutions
Universe
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- Describe the characteristics of the various kinds of interstellar gas (HII regions, neutral hydrogen clouds, ultra-hot gas clouds, and molecular clouds).arrow_forwardHow does the presence of an active galactic nucleus in a starburst galaxy affect the starburst process?arrow_forwardPictures of various planetary nebulae show a variety of shapes, but astronomers believe a majority of planetary nebulae have the same basic shape. How can this paradox be explained?arrow_forward
- Why does star formation occur primarily in the disk of the Galaxy?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_forwardWhy do molecules, including H2 and more complex organic molecules, only form inside dark clouds? Why don’t they fill all interstellar space?arrow_forward
- A 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_forwardHow 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_forwardUsing the same techniques as used in Exercise 19.32, how far away can Gaia be used to measure distances with an uncertainty of 10%? What fraction of the Galactic disk does this correspond to?arrow_forward
- If the Sun were a member of the cluster NGC 2264, would it be on the main sequence yet? Why or why not?arrow_forwardWhy do nebulae near hot stars look red? Why do dust clouds near stars usually look blue?arrow_forwardAt the low temperature found in some interstellar molecular clouds (around 100 K), molecular oxygen emission is strongest at a wavelength of 0.2521 cm. Determine the speed (in km/s) of a low temperature molecular cloud containing molecular oxygen if its strongest emission is at a wavelength of 0.1885 cm. Note that this cloud is moving towards us, so the answer should be negative.arrow_forward
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