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 23, Problem 18Q
To determine
Importance of Type Ia supernova when finding the distances to very remote galaxies and the limitations of using Type Ia supernova in this process.
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An observational survey of distant galaxies is undertaken that involves measuring their
distances using cepheid variables and red-shifts using spectroscopy. Explain how cepheid
variables can be used to measure the distances to galaxies.
A spectral line is observed whose wavelength in the laboratory is de
length of this spectral line observed in each galaxy, Xo, is listed in the table, along with
the distance, d, to the galaxy. Determine the red-shift and the recession velocity of each
galaxy and tabulate your results by making a copy of the table and filling in the blank spaces.
Sketch a Hubble diagram using your results and determine the value of the Hubble constant
Ho in units of km s-1 Mpc.
650 nm. The wave-
Galaxy 1
652.69
Galaxy 2 Galaxy 3 Galaxy 4 Galaxy 5
653.01
do (nm)
d (Mpc)
658.54
662.18
681.63
17
19
54
77
200
v (km s-1)
Consider a galaxy with a density profile of the type
Ро
p(r)
=
(r/ro)[(1+r/ro)²] '
where po is the central density.
1. In a sentence describe what ro represents.
2. Find the mass profile M(r) for such a galaxy.
3. Find the circular velocity profile (r) for such a galaxy.
How astronomers determine the distance of a galaxy? Explain.
Chapter 23 Solutions
Universe: Stars And Galaxies
Ch. 23 - Prob. 1QCh. 23 - Prob. 2QCh. 23 - Prob. 3QCh. 23 - Prob. 4QCh. 23 - Prob. 5QCh. 23 - Prob. 6QCh. 23 - Prob. 7QCh. 23 - Prob. 8QCh. 23 - Prob. 9QCh. 23 - Prob. 10Q
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- Given that only about 5% of the galaxies visible in the Hubble Deep Field are bright enough for astronomers to study spectroscopically, they need to make the most of the other 95%. One technique is to use their colors and apparent brightnesses to try to roughly estimate their redshift. How do you think the inaccuracy of this redshift estimation technique (compared to actually measuring the redshift from a spectrum) might affect our ability to make maps of large-scale structures such as the filaments and voids shown in Figure 28.21? Figure 28.21 Sloan Digital Sky Survey Map of the Large-Scale Structure of the Universe. This image shows slices from the SDSS map. The point at the center corresponds to the Milky Way and might say “You Are Here!” Points on the map moving outward from the center are farther away. The distance to the galaxies is indicated by their redshifts (following Hubble’s law), shown on the horizontal line going right from the center. The redshift z=/ , where is the difference between the observed wavelength and the wavelength emitted by a nonmoving source in the laboratory. Hour angle on the sky is shown around the circumference of the circular graph. The colors of the galaxies indicate the ages of their stars, with the redder color showing galaxies that are made of older stars. The outer circle is at a distance of two billion light-years from us. Note that red (older stars) galaxies are more strongly clustered than blue galaxies (young stars). The unmapped areas are where our view of the universe is obstructed by dust in our own Galaxy. (credit: modification of work by M. Blanton and the Sloan Digital Sky Survey)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_forwardWhat are the two best ways to measure the distance to a distant, isolated spiral galaxy, and how would it be measured?arrow_forward
- Please answer within 90 minutes.arrow_forwardWhat are the characteristics of an E7 Galaxy? What about E0 galaxy? Explain.arrow_forwardEach point on the above diagram shows the line-of-sight recession velocity versus distance for a number of distant galaxies. Describe how the recession velocities of galaxies are measured by astronomers. Explain the different techniques used by astronomers to measure the distances to galaxies, and describe how these methods are used to construct the distance ladder.arrow_forward
- Assume that we have measured the distance to a close by galaxy, with apparent magnitude m1 = 6, to be d1 = 1Mpc. We now assume that all galaxies are similar and have therefore the same intrinsic or absolute, luminosity. Then measuring the apparent magnitude of a second galaxy to be m2 = 11, estimate the distance to that galaxy. Please answer within 90 minutes.arrow_forwardA galaxy with a spherically symmetric distribution of matter has a mass density profile of the type p(r) ∞ 1/r, where r is the radial coordinate from the centre of the galaxy. To what type of circular velocity (r) does this correspond? Select one: a. (r) O b. c. O d. (r) ~ r (r) ~ √r (r): = constantarrow_forwardIndicate whether the following statements are true or false. (Select T-True, F-False. If the first is T and the rest F, enterTFFFFF). A) The three main classifications of galaxies are elliptical, spiral and prime.B) The mass of a spiral galaxy can be found from its rotational velocity. The greater the rotation, the greater the mass.C) Galaxies sometimes collide with each other.D) It wasn't until the 1920s that we knew the Milky Way was only one of many galaxies.E) Most galaxies are elliptical.F) The shorter the pulsation period of a Cepheid variable star, the more luminous it is.arrow_forward
- 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?arrow_forwardThe surface brightness profiles of elliptical galaxies follow the Sersic formula with n = 4. How much fainter is the elliptical galaxy at a radius of r compared r0 (the radius at which the brightness falls off by a factor of e), or in other words, what is the ratio of I(r)/I0. Values: r = 14 r0arrow_forwardWhat are potential solutions to the missing satellites problem (i.e. solutions that solve the problem without discarding ACDM)? (Choose 3). O If simulations include a Galactic potential, fewer dark matter halos survive. Many low-mass galaxies exist, but are not bright enough to be seen by current telescopes. O Low mass galaxies merge into large galaxies and become part of their stellar halos. O The number of low mass dark matter halos that form is lower than predictions based on cosmological initial conditions. O lonizing photons from the first stars, galaxies or quasars heat gas until the pressure is too high to collapse into the smallest dark matter halos. O Dwarf galaxies stream out of voids and into clusters and superclusters where they merge into larger galaxies.arrow_forward
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