Astronomy
1st Edition
ISBN: 9781938168284
Author: Andrew Fraknoi; David Morrison; Sidney C. Wolff
Publisher: OpenStax
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Textbook Question
Chapter 26, Problem 23E
Suppose you were Hubble and Humason, working on the distances and Doppler shifts of the galaxies. What sorts of things would you have to do to convince yourself (and others) that the relationship you were seeing between the two quantities was a real feature of the behavior of the universe? (For example, would data from two galaxies be enough to demonstrate Hubble’s law? Would data from just the nearest galaxies-in what astronomers call “the Local Group”-suffice?)
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Chapter 26 Solutions
Astronomy
Ch. 26 - Describe the main distinguishing features of...Ch. 26 - Why did it take so long for the existence of other...Ch. 26 - Explain what the mass-to-light ratio is and why it...Ch. 26 - If we now realize dwarf ellipticals are the most...Ch. 26 - What are the two best ways to measure the distance...Ch. 26 - What are the two best ways to measure the distance...Ch. 26 - Why is Hubble’s law considered one of the most...Ch. 26 - What does it mean to say that the universe is...Ch. 26 - Was Hubble’s original estimate of the distance to...Ch. 26 - Does an elliptical galaxy rotate like a spiral...
Ch. 26 - Why does the disk of a spiral galaxy appear dark...Ch. 26 - What causes the largest mass-to-light ratio: gas...Ch. 26 - What is the most useful standard bulb method for...Ch. 26 - When comparing two isolated spiral galaxies that...Ch. 26 - If all distant galaxies are expanding away from...Ch. 26 - Is the Hubble constant actually constant?Ch. 26 - Where might the gas and dust (if any) in an...Ch. 26 - Why can we not determine distances to galaxies by...Ch. 26 - Which is redder-a spiral galaxy or an elliptical...Ch. 26 - Suppose the stars in an elliptical galaxy all...Ch. 26 - Starting with the determination of the size of...Ch. 26 - Suppose the Milky Way Galaxy were truly isolated...Ch. 26 - Suppose you were Hubble and Humason, working on...Ch. 26 - What does it mean if one elliptical galaxy has...Ch. 26 - Based on your analysis of galaxies in Table 26.1,...Ch. 26 - Can a higher mass-to-light ratio mean that there...Ch. 26 - According to Hubble’s law, what is the recessional...Ch. 26 - A cluster of galaxies is observed to have a...Ch. 26 - Suppose we could measure the distance to a galaxy...Ch. 26 - Calculate the mass-to-light ratio for a globular...Ch. 26 - Calculate the mass-to-light ratio for a luminous...
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- Why don’t any of the methods for establishing distances to galaxies, described in Galaxies (other than Hubble’s law itself), work for quasars?arrow_forwardGiven 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_forwardDescribe the arguments supporting the idea that quasars are at the distances indicated by their redshifts.arrow_forward
- Show that no matter how big a redshift (z) we measure, v/c will never be greater than 1. (In other words, no galaxy we observe can be moving away faster than the speed of light.)arrow_forwardOnce again in this chapter, we see the use of Kepler’s third law to estimate the mass of supermassive black holes. In the case of NGC 4261, this chapter supplied the result of the calculation of the mass of the black hole in NGC 4261. In order to get this answer, astronomers had to measure the velocity of particles in the ring of dust and gas that surrounds the black hole. How high were these velocities? Turn Kepler’s third law around and use the information given in this chapter about the galaxy NGC 4261-the mass of the black hole at its center and the diameter of the surrounding ring of dust and gas-to calculate how long it would take a dust particle in the ring to complete a single orbit around the black hole. Assume that the only force acting on the dust particle is the gravitational force exerted by the black hole. Calculate the velocity of the dust particle in km/s.arrow_forwardIt is possible to derive the age of the universe given the value of the Hubble constant and the distance to a galaxy, again with the assumption that the value of the Hubble constant has not changed since the Big Bang. Consider a galaxy at a distance of 400 million light-years receding from us at a velocity, v. If the Hubble constant is 20 km/s per million light-years, what is its velocity? How long ago was that galaxy right next door to our own Galaxy if it has always been receding at its present rate? Express your answer in years. Since the universe began when all galaxies were very close together, this number is a rough estimate for the age of the universe.arrow_forward
- Suppose somebody proposed that rather than invoking dark matter to explain the increased orbital velocities of stars beyond the Sun’s orbit, the problem could be solved by assuming that the Milky Way’s central black hole was much more massive. Does simply increasing the assumed mass of the Milky Way’s central supermassive black hole correctly resolve the issue of unexpectedly high orbital velocities in the Galaxy? Why or why not?arrow_forwardIn the chapter, we discussed that the largest redshifts found so far are greater than 6. Suppose we find a quasar with a redshift of 6.1. With what fraction of the speed of light is it moving away from us?arrow_forwardWhat does the term Hubble time mean in cosmology, and what is the current best calculation for the Hubble time?arrow_forward
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