Foundations of Astronomy (MindTap Course List)
14th Edition
ISBN: 9781337399920
Author: Michael A. Seeds, Dana Backman
Publisher: Cengage Learning
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Chapter 15, Problem 2RQ
To determine
The reason behind the exact dimension of the Galaxy’s disk and visible halo are hard to determine.
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A given star orbits the center of its galaxy at an average speed of v_star, at a distance of r_star from the center. The galaxy has 2 spiral arms, and the arms themselves orbit slower than the star -- at the same radius, they orbit at a speed of v_arm (in the same direction as the star). The galaxy's age is t_gal. In the history of this galaxy, how many times did this star cross through a spiral arm?
Values: v_star = 200 km/s, r_star = 9 kpc, v_arms = 46 km/s, t_gal = 4 Gyr
Given an image of a disk galaxy, you have measured that the average surface brightness at two radii (R = R1 and R = R2) are I1 and I2 respectively. The disk surface brightness profile has the exponential form of I(R) = I0 e(-R/Rd).
What are the values of I0 and Rd for this disk?
Among the globular clusters orbiting a distant galaxy, one is moving at 534 km/s and is located 14 kpc from the center of the galaxy. Assuming the globular cluster is located outside most of the mass of the galaxy, what is the mass of the galaxy? Convert your answer to solar masses. (Hint: Use the formula for circular velocity,
Vc =
GM
r
;
make sure you convert relevant quantities to units of meters, kilograms, and seconds. Note: 1 pc = 3.1 ✕ 1016 m.)
Chapter 15 Solutions
Foundations of Astronomy (MindTap Course List)
Ch. 15 - What evidence can you give that we live in a...Ch. 15 - Prob. 2RQCh. 15 - Why didnt astronomers before Shapley realize how...Ch. 15 - Prob. 4RQCh. 15 - Prob. 5RQCh. 15 - Prob. 6RQCh. 15 - Which parts of a spiral galaxy comprise the...Ch. 15 - Prob. 8RQCh. 15 - Prob. 9RQCh. 15 - Prob. 10RQ
Ch. 15 - Prob. 11RQCh. 15 - Prob. 12RQCh. 15 - Prob. 13RQCh. 15 - Prob. 14RQCh. 15 - Prob. 15RQCh. 15 - Prob. 16RQCh. 15 - Prob. 17RQCh. 15 - Prob. 18RQCh. 15 - Prob. 19RQCh. 15 - Prob. 20RQCh. 15 - Prob. 21RQCh. 15 - Prob. 22RQCh. 15 - Prob. 23RQCh. 15 - Prob. 24RQCh. 15 - Prob. 25RQCh. 15 - Prob. 26RQCh. 15 - Rank these objects from oldest to youngest the...Ch. 15 - What evidence contradicts the top-down hypothesis...Ch. 15 - Prob. 29RQCh. 15 - The story of a process makes the facts easier to...Ch. 15 - Prob. 1PCh. 15 - Prob. 2PCh. 15 - Prob. 3PCh. 15 - Prob. 4PCh. 15 - Prob. 5PCh. 15 - Prob. 6PCh. 15 - Prob. 7PCh. 15 - Prob. 8PCh. 15 - If the Sun is 4.6 billion years old, how many...Ch. 15 - Prob. 10PCh. 15 - Prob. 11PCh. 15 - Prob. 12PCh. 15 - Prob. 13PCh. 15 - Prob. 14PCh. 15 - Prob. 15PCh. 15 - Prob. 1SOPCh. 15 - Prob. 2SOPCh. 15 - Prob. 2LTLCh. 15 - Prob. 3LTLCh. 15 - Prob. 4LTLCh. 15 - Prob. 5LTL
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- Why does the disk of a spiral galaxy appear dark when viewed edge on?arrow_forwardSuppose three stars lie in the disk of the Galaxy at distances of 20,000 light-years, 25,000 light-years, and 30,000 light-years from the galactic center, and suppose that right now all three are lined up in such a way that it is possible to draw a straight line through them and on to the center of the Galaxy. How will the relative positions of these three stars change with time? Assume that their orbits are all circular and lie in the plane of the disk.arrow_forwardThe best parallaxes obtained with Hipparcos have an accuracy of 0.001 arcsec. If you want to measure the distance to a star with an accuracy of 10%, its parallax must be 10 times larger than the typical error. How far away can you obtain a distance that is accurate to 10% with Hipparcos data? The disk of our Galaxy is 100,000 light-years in diameter. What fraction of the diameter of the Galaxy’s disk is the distance for which we can measure accurate parallaxes?arrow_forward
- Consider the following data on four stars: Which star would have the largest radius? Which star would have the smallest radius? Which star is the most common in our area of the Galaxy? Which star is the least common?arrow_forwardLook back at Figure 6.18 of Cygnus A and read its caption again. The material in the giant lobes at the edges of the image had to have been ejected from the center at least how many years ago? Figure 6.18 Radio Image. This image has been constructed of radio observations at the Very Large Array of a galaxy called Cygnus A. Colors have been added to help the eye sort out regions of different radio intensities. Red regions are the most intense, blue the least. The visible galaxy would be a small dot in the center of the image. The radio image reveals jets of expelled material (more than 160,000 light-years long) on either side of the galaxy. (credit: NRAO/AUI)arrow_forwardIf the diameter of the Milky Way Galaxys visible disk, 80,000 ly, is represented in a model by a dinner plate with a diameter of 10 inches, what is the model distance to galaxy M31, 2.6 millionly away? What is the model distance to the Virgo galaxy cluster, 16 Mpc away? (Convert answers to feet.)arrow_forward
- Describe how you might use the color of a galaxy to determine something about what kinds of stars it contains.arrow_forwardAssume that dark matter is uniformly distributed throughout the Milky Way, not just in the outer halo but also throughout the bulge and in the disk, where the solar system lives. How much dark matter would you expect there to be inside the solar system? Would you expect that to be easily detectable? Hint: For the radius of the Milky Way’s dark matter halo, use R=300,000 light-years; for the solar system’s radius, use 100 AU; and start by calculating the ratio of the two volumes.arrow_forwardThe center of a faint but active galaxy has magnitude 26. How much less bright does it look than the very faintest star that our eyes can see, roughly magnitude 6?arrow_forward
- Among the globular clusters orbiting a distant galaxy, one is moving at 417 km/s and is located 16 kpc from the center of the galaxy. Assuming the globular cluster is located outside most of the mass of the galaxy, what is the mass of the galaxy? Convert your answer to solar masses. (Hint: Use the formula for circular velocity, V, = V GM ; make sure you convert relevant quantities to units of meters, kilograms, and seconds. Note: 1 pc = 3.1 x 1016 m.) solar masses (M.)arrow_forwardThe figure below shows the spectra of two galaxies A and B.arrow_forwardThe Tully-Fischer method relies on being able to relate the mass of a galaxy to its rotation velocity. Stars in the outer-most regions of the Milky Way galaxy, located at a distance of 50 kpc from the galactic centre, are observed to orbit at a speed vrot = 250 km s−1. Using Kepler’s 3rd Law, determine the mass in the Milky Way that lies interior to 50 kpc. Express your answer in units of the Solar mass.arrow_forward
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