Astronomy
1st Edition
ISBN: 9781938168284
Author: Andrew Fraknoi; David Morrison; Sidney C. Wolff
Publisher: OpenStax
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Textbook Question
Chapter 26, Problem 22E
Suppose the Milky Way Galaxy were truly isolated and that no other galaxies existed within 100 million light-years. Suppose that galaxies were observed in larger numbers at distances greater than 100 million light-years. Why would it be more difficult to determine accurate distances to those galaxies than if there were also galaxies relatively close by?
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Suppose you want to observe every galaxy within
some distance. Your enterprising assistant says that
instead you can observe every galaxy within double
the original distance. What is the ratio of the number
of galaxies you can now observe as opposed to
before? (For example, if you can observe twice as
many: 2. If you can observe half as many: 0.5)
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Suppose you want to observe every galaxy within some distance. Your enterprising assistant says that instead you can observe every galaxy within double the original distance. What is the ratio of the number of galaxies you can now observe as opposed to before?
In the reading, you were told that there were roughly 10,000 galaxies in the image of the Hubble Ultra Deep Field alone. The image is roughly 10 square arcminutes and there are roughly 1.5*10^8 square arcminutes composing the entire sky. With that in mind and assuming that the Hubble Ultra Deep Field represents an average part of the sky, roughly how many galaxies may exist in the observable universe? (Please include commas for every factor of 1,000; for example 2,343,567,890)
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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- Suppose 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_forwardIf we now realize dwarf ellipticals are the most common type of galaxy, why did they escape our notice for so long?arrow_forwardOur galaxy is approximately 100,000 light years in diameter and 2,000 light years thick through the plane of the galaxy. If we were to compare the ratio of the diameter galaxy and its thickness to the ratio of the diameter of a CD and its thickness (CD has a diameter of 12 cm and thickness of 0.6 mm), what would be the factor differentiating those ratios? Put differently, if the galaxy were scaled down to the diameter of a CD, how many times thicker or thinner would the galaxy be than the CD? (For example if it would be twice as thick, you would answer 2 and if it were twice as thin you would answer 0.5 (aka 1/2))arrow_forward
- Let's say that the number density of galaxies in the universe is, on average, 3 × 10–68 galaxies/m3. If astronomers could observe all galaxies out to a distance of 1010 light-years, how many galaxies would they find? (Note that there are 1016 meters in 1 light-year.)arrow_forwardIf the active core of a galaxy contains a black hole of 106?Θ (1 million solar masses), what will the orbital velocity be for matter orbiting the black hole at a distance of 0.33 AU? (Hint: use the formula for orbital velocity: ?=√???; where ?=6.67×10−11 ?3?? ?2 and ?Θ= 2.0×1030 ??. Note: 1 ??=1.50×1011 ?)arrow_forwardIf a galaxy is 8.9 Mpc away from Earth and recedes at 497 km/s, what is H. (in km/s/Mpc)? km/s/Mрс What is the Hubble time (in yr)? years How old (in yr) would the universe be, assuming space-time is flat and the expansion of the universe has not been accelerating? years How would acceleration change your answer? If the expansion of the Universe has been accelerating, the Universe could be substantially younger than the value entered above. If the expansion of the Universe has been accelerating, the Universe could be substantially older than the value entered above.arrow_forward
- How astronomers determine the distance of a galaxy? Explain.arrow_forwardAstronomers recently claimed to have discovered the most distant galaxy known. How would they have determine this distance?arrow_forwardAssume that a typical galaxy contains about 200 billion stars and that there are more than 150 billion galaxies in the known universe. Estimate the total number of stars in the universe.arrow_forward
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