26.11.2: Thought Questions
Thought Questions
Where might the gas and dust (if any) in an elliptical galaxy come from?
18.
Why can we not determine distances to galaxies by the same method used to measure the parallaxes of stars?
19.
Which is redder—a spiral galaxy or an elliptical galaxy?
20.
Suppose the stars in an elliptical galaxy all formed within a few million years shortly after the universe began. Suppose these stars have a range of masses, just as the stars in our own galaxy do. How would the color of the elliptical change over the next several billion years? How would its luminosity change? Why?
21.
Starting with the determination of the size of Earth, outline a sequence of steps necessary to obtain the distance to a remote cluster of galaxies. (Hint: Review the chapter on Celestial Distances.)
22.
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?
23.
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?)
24.
What does it mean if one elliptical galaxy has broader spectrum lines than another elliptical galaxy?
25.
Based on your analysis of galaxies in Table 26.1, is there a correlation between the population of stars and the quantity of gas or dust? Explain why this might be.
26.
Can a higher mass-to-light ratio mean that there is gas and dust present in the system that is being analyzed?