Assignment 20 - Galaxies & Cosmology

25 July 2022
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question
Following are a number of distinguishing characteristics of spiral and elliptical galaxies. Match each characteristic to the appropriate galaxy type.
answer
Spiral galaxies 1. have a flattened disk of stars 2. are rare in central regions of galaxy clusters 3. contain many bright, hot stars 4. contain abundant clouds of cool gas and dust 5. have significant, ongoing star formation Elliptical galaxies 1. contain primarily old, low-mass stars 2. are more reddish in color
question
Match the terms in the left-hand column to the appropriate blank in the sentences in the right-hand column. Use each term only once.
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1. The globular cluster M13 belongs to the halo component of the Milky Way Galaxy. 2. A(n) elliptical galaxy contains hot, ionized gas but very little cool gas or dust. 3. The type of galaxy known as a(n)irregular galaxy was more common in the universe 10 billion years ago. 4. The Milky Way is a(n) spiral galaxy. 5. Our Sun belongs to the disk component of the Milky Way Galaxy. 6. Scientists investigating cosmology study how the distribution of galaxies changes with time.
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Why is the Hyades Cluster important for building up a catalog of the true luminosities of main-sequence stars?
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It is close enough to us that the distance to the cluster stars can be found by stellar parallax.
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Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities. Hence, we can use Cepheids as "standard candles" for distance measurements.
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Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities. Hence, we can use Cepheids as "standard candles" for distance measurements.
question
You observe the peak brightnesses of two white dwarf supernovae. Supernova A is only one-quarter as bright as Supernova B. What can you say about their relative distances?
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Supernova A is twice as far away as Supernova B.
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Which kind of object is the best standard candle for measuring distances to extremely distant galaxies?
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a white dwarf supernova
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What does Hubble's law tell us?
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The more distant a galaxy, the faster it is moving away from us.
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Spectral lines from Galaxy B are redshifted from their rest wavelengths twice as much as the spectral lines from Galaxy A. According to Hubble's law, what can you say about their approximate relative distances?
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Galaxy B is twice as far as Galaxy A.
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Why do virtually all the galaxies in the universe appear to be moving away from our own?
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Observers in all galaxies observe a similar phenomenon because of the universe's expansion.
question
The following figures give the approximate distances of five galaxies from Earth. Rank the galaxies based on the speed with which each should be moving away from Earth due to the expansion of the universe, from fastest to slowest.
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Fastest to Slowest 5 billion light-years 2 billion light-years 800 million light-years 230 million light-years 70 million light-years
question
The following figures give the approximate speeds at which five galaxies are moving away from Earth due to the expansion of the universe. Rank the galaxies based on their distance from Earth, from farthest to closest.
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Farthest to Closest 130,000 km/s 45,000 km/s 18,730 km/s 5,264 km/s 1,577 km/s
question
The following figures give the approximate speeds at which five galaxies are moving away from Earth due to the expansion of the universe. Rank the galaxies based on the amount of redshift that would be observed in each galaxy's spectrum, from largest to smallest.
answer
Largest redshift to Smallest reshift 130,000 km/s 45,000 km/s 18,730 km/s 5,264 km/s 1,577 km/s
question
Hubble's law is a relationship between galaxy speeds and galaxy distances. This relationship can be shown as a line on a graph of speed versus distance. Each of the following four graphs shows a possible relationship expressing Hubble's law. Rank the graphs based on their predictions of the speed, from fastest to slowest, for a galaxy located 400 million light-years away from Earth.
answer
Fastest to Slowest -Speed away from Earth (km/s) 30000, Distance from Earth (millions of light-years) 400 -Speed away from Earth (km/s) 30000, Distance from Earth (millions of light-years) 600 -Speed away from Earth (km/s) 20000, Distance from Earth (millions of light-years) 1000 -Speed away from Earth (km/s) 15000, Distance from Earth (millions of light-years) 1200
question
The following four graphs are the same as those from Part D, with each showing a possible relationship for Hubble's law. Rank the graphs based on the prediction they each would make for the current age of the universe, from oldest to youngest.
answer
-Speed away from Earth (km/s) 15000, Distance from Earth (millions of light-years) 1200 -Speed away from Earth (km/s) 20000, Distance from Earth (millions of light-years) 1000 -Speed away from Earth (km/s) 30000, Distance from Earth (millions of light-years) 600 -Speed away from Earth (km/s) 30000, Distance from Earth (millions of light-years) 400
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Based on counting the number of galaxies in a small patch of the sky and multiplying by the number of such patches needed to cover the entire sky, the total number of galaxies in the observable universe is estimated to be approximately
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100 billion.
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How was Edwin Hubble able to use his discovery of a Cepheid in Andromeda to prove that the "spiral nebulae" were actually entire galaxies?
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From the period-luminosity relation for Cepheids, he was able to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy.
question
Which of the following sequences lists the methods for determining distance in the correct order from nearest to farthest?
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parallax, main-sequence fitting, Cepheid variables, Tully-Fisher relation, Hubble's law
question
Based on current estimates of the value of Hubble's constant, how old is the universe?
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between 12 and 16 billion years old