Astronomy
1st Edition
ISBN: 9781938168284
Author: Andrew Fraknoi; David Morrison; Sidney C. Wolff
Publisher: OpenStax
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Textbook Question
Chapter 26, Problem 14E
When comparing two isolated spiral galaxies that have the same apparent brightness, but rotate at different rates, what can you say about their relative luminosity?
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An astronomical image shows two objects that have the same apparent magnitude, i.e., the same brightness. However, spectroscopic follow up observations indicate that while one is a star that is within our galaxy, at a distance dgal away, and has the same luminosity as the Sun, the other is a quasar and has 100x the luminosity of the entire Milky Way galaxy. What is the distance to the quasar? (You may assume, for this rough calculation, that the Milky Way has 1011 stars and that they all have the luminosity as the Sun.) Give your response in Mpc. Value: dgal = 49 pc
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The Hubble Law, equation (D), can be used to determine the age of the universe. Using your average valueof H, calculate the recessional velocity of a galaxy of a galaxy which is 800 Mpc away.Velocity of a galaxy 800 Mpc away: _______________________________km/sec
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 can we not determine distances to galaxies by the same method used to measure the parallaxes of stars?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_forwardWhich is likely to be more common in our Galaxy: white dwarfs or black holes? Why?arrow_forward
- The center of our Galaxy is about 7500 parsecs from Earth. What would be the parallax angle of a star near the center of the Galaxy? Could this angle be measured with current technology?arrow_forwardWhen two galaxies collide, the stars inside them are not likely to be much affected, because the __________ stars is so large compared to their diameters. However, the _______ of stars and gas can be changed, altering the appearance of the galaxies. Astronomers have determined that such collisions are seen more often in ____________. When two galaxies of roughly equal size collide, astronomers call it a _______ of galaxies; but when a small galaxy collides with a much larger one, the process is called ___________. When a galaxy has a significant amount of its interstellar gas compressed by a collision, leading to the birth of many new stars, astronomers call it a __________ galaxy.arrow_forwardAn 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)arrow_forward
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