Universe: Stars And Galaxies
6th Edition
ISBN: 9781319115098
Author: Roger Freedman, Robert Geller, William J. Kaufmann
Publisher: W. H. Freeman
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Chapter 26, Problem 35Q
To determine
The difference between hot and cold dark matter and the way to decide the one that was important in the formation of large scale structure like the cluster of galaxies.
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Are the galaxies red-shifting or blue-shifting? Explain. (You may find the big-bang theory helpful). Andromeda galaxy is currently approaching our galaxy with a radial velocity of 266 km/sec. How far is our galaxy from Andromeda? (Hubble’s constant, H, is 73 km/sec/MParsec). When can the two galaxies be anticipated to collide?
Choose the statement that is NOT true of a galaxy.
O Galaxies take different shapes depending on how the stars are distributed and oriented.
O Agreat island of stars held together by gravity.
All galaxies are basically of the same shape and consist mainly of a discs and a halos.
All the stars in a galary orbit a common center
Astronomers now think that there is a black hole with more than 4 milliion times the mass of our Sun at the center of our galaxy?
Roughly how large would the event horizon of such a supermassive black hole be?
a. the size of our moon
b. about 4 light years across
c. about 17 times the size of our sun
d. about the size of an atom (so much mass really compresses the event horizon)
e. this question can't be answered without knowing what kind of stars were swallowed by the black hole
Chapter 26 Solutions
Universe: Stars And Galaxies
Ch. 26 - Prob. 1QCh. 26 - Prob. 2QCh. 26 - Prob. 3QCh. 26 - Prob. 4QCh. 26 - Prob. 5QCh. 26 - Prob. 6QCh. 26 - Prob. 7QCh. 26 - Prob. 8QCh. 26 - Prob. 9QCh. 26 - Prob. 10Q
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- How astronomers determine the distance of a galaxy? Explain.arrow_forwardA galaxy's rotation curve is a measure of the orbital speed of stars as a function of distance from the galaxy's centre. The fact that rotation curves are primarily flat at large galactocen- tric distances (vrot(r) ~ constant) is the most common example of why astronomer's believe dark matter exists. Let's work out why! Assuming that each star in a given galaxy has a circular orbit, we know that the accelera- tion due to gravity felt by each star is due to the mass enclosed within its orbital radius r and equal to v?/r. Here, ve is the circular orbit velocity of the star. (a) Show that the expected relationship between ve and r due to the stellar halo (p(r) xr-3.5) does not produce a flat rotation curve. (b) Show that a p(r) ∞ r¯² density profile successfully produces a flat ro- tation curve and must therefore be the general profile that dark matter follows in our galaxy.arrow_forwardAn astronomer observed the motions of some galaxies. Based on his observations, he made the following statements. Which one of them is most likely to be false? Take Hubble's constant to be 67 km/s/Mpc. A. A galaxy observed to be moving away from us at a speed of 70 km/s is at a distance of about 1 Mpc from us. B. A galaxy observed to be moving away from us at a speed of 700 km/s is at a distance of about 10 Mpc from us. C. A galaxy observed to be moving away from us at a speed of 7000 km/s is at a distance of about 100 Mpc from us. D. A galaxy observed to be moving away from us at a speed of 70000 km/s is at a distance of about 1 Gpc from us. Is the answer D? Thank you!arrow_forward
- Suppose the stars in an elliptical galaxy all formed within a few million years shortly after the universe began. Suppose these stars have a range of masses, just as the stars in our own galaxy do. How would the color of the elliptical change over the next several billion years? How would its luminosity change? Why?arrow_forwardCan an elliptical galaxy evolve into a spiral? Explain your answer. Can a spiral turn into an elliptical? How?arrow_forwardThe first clue that the Galaxy contains a lot of dark matter was the observation that the orbital velocities of stars did not decreases with increasing distance from the center of the Galaxy. Construct a rotation curve for the solar system by using the orbital velocities of the planets, which can be found in Appendix F. How does this curve differ from the rotation curve for the Galaxy? What does it tell you about where most of the mass in the solar system is concentrated?arrow_forward
- Does an elliptical galaxy rotate like a spiral galaxy? Explain.arrow_forwardAssume that the Sun orbits the center of the Galaxy at a speed of 220 km/s and a distance of 26,000 lightyears from the center. A. Calculate the circumference of the Sun’s orbit, assuming it to be approximately circular. (Remember that the circumference of a circle is given by 2pR, where R is the radius of the circle. Be sure to use consistent units. The conversion from light-years to km/s can be found in an online calculator or appendix, or you can calculate it for yourself: the speed of light is 300,000 km/s, and you can determine the number of seconds in a year.) B. Calculate the Sun’s period, the “galactic year.” Again, be careful with the units. Does it agree with the number we gave above?arrow_forwardWhat are the two best ways to measure the distance to a nearby spiral galaxy, and how would it be measured?arrow_forward
- Explain what the mass-to-light ratio is and why it is smaller in spiral galaxies with regions of star formation than in elliptical galaxies.arrow_forwardThe globular clusters revolve around the Galaxy in highly elliptical orbits. Where would you expect the clusters to spend most of their time? (Think of Kepler’s laws.) At any given time, would you expect most globular clusters to be moving at high or low speeds with respect to the center of the Galaxy? Why?arrow_forwardExplain where in a spiral galaxy you would expect to find globular clusters, molecular clouds, and atomic hydrogen.arrow_forward
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