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Table of Contents
1 What’s in the Dark?
Astronomers use a variety of intellectual tools to study objects they cannot touch or even see.
2 When Mass Is Like Glass
Gravitational lensing can be understood through an analogy with a glass lens shaped like the base of a wine glass.
3 How Do You Weigh a Galaxy?
The motions of stars and light rays probe a galaxy’s gravitational field, and hence its mass.
4 Is Dark Matter MACHO or WIMPy?
Gravitational lensing within our galaxy helped demonstrate that dark matter is not just normal matter that is hard to see. It must be something exotic, which physicists are now trying to catch.
5 Finding What’s Missing
Conventional dark matter theory predicts that galaxies are surrounded by invisible clumps of dark matter. Lensing can help find them.
6 “A Long Time Ago in a Galaxy Far, Far Away”
Clusters of galaxies act as cosmic telescopes, helping astronomers study distant objects that would otherwise be too small and faint to see.
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