Mindblown: a blog about philosophy.
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The Formation and Evolution of Galaxies and Structure in the Universe
Learning Objectives By the end of this section, you will be able to: As with most branches of natural science, astronomers and cosmologists always want to know the answer to the question, “How did it get that way?” What made galaxies and galaxy clusters, superclusters, voids, and filaments look the way they do? The existence…
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The Challenge of Dark Matter
Learning Objectives By the end of this section, you will be able to: So far this chapter has focused almost entirely on matter that radiates electromagnetic energy—stars, planets, gas, and dust. But, as we have pointed out in several earlier chapters (especially The Milky Way Galaxy), it is now clear that galaxies contain large amounts of…
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The Distribution of Galaxies in Space
Learning Objectives By the end of this section, you will be able to: In the preceding section, we emphasized the role of mergers in shaping the evolution of galaxies. In order to collide, galaxies must be fairly close together. To estimate how often collisions occur and how they affect galaxy evolution, astronomers need to know…
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Galaxy Mergers and Active Galactic Nuclei
Learning Objectives By the end of this section, you will be able to: One of the conclusions astronomers have reached from studying distant galaxies is that collisions and mergers of whole galaxies play a crucial role in determining how galaxies acquired the shapes and sizes we see today. Only a few of the nearby galaxies…
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Observations of Distant Galaxies
Learning Objectives By the end of this section, you will be able to: Let’s begin by exploring some techniques astronomers use to study how galaxies are born and change over cosmic time. Suppose you wanted to understand how adult humans got to be the way they are. If you were very dedicated and patient, you could actually…
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Thinking Ahead
How and when did galaxies like our Milky Way form? Which formed first: stars or galaxies? Can we see direct evidence of the changes galaxies undergo over their lifetimes? If so, what determines whether a galaxy will “grow up” to be spiral or elliptical? And what is the role of “nature versus nurture”? That is…
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Quasars as Probes of Evolution in the Universe
Learning Objectives By the end of this section, you will be able to: The quasars’ brilliance and large distance make them ideal probes of the far reaches of the universe and its remote past. Recall that when first introducing quasars, we mentioned that they generally tend to be far away. When we see extremely distant…
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Supermassive Black Holes: What Quasars Really Are
Learning Objectives By the end of this section, you will be able to: In order to find a common model for quasars (and their cousins, the AGNs), let’s first list the common characteristics we have been describing—and add some new ones: The readers of this text are in a much better position than the astronomers who…
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Quasars
Learning Objectives By the end of this section, you will be able to: The name “quasars” started out as short for “quasi-stellar radio sources” (here “quasi-stellar” means “sort of like stars”). The discovery of radio sources that appeared point-like, just like stars, came with the use of surplus World War II radar equipment in the…
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Thinking Ahead
During the first half of the twentieth century, astronomers viewed the universe of galaxies as a mostly peaceful place. They assumed that galaxies formed billions of years ago and then evolved slowly as the populations of stars within them formed, aged, and died. That placid picture completely changed in the last few decades of the…
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