The Mass of the Galaxy
Learning Objectives By the end of this section, you will be able to: When we described the sections of the Milky Way, we said that the stars are now known to be surrounded by a much larger halo of invisible…
Spiral Structure
Learning Objectives By the end of this section, you will be able to: Astronomers were able to make tremendous progress in mapping the spiral structure of the Milky Way after the discovery of the 21-cm line that comes from cool hydrogen (see Between…
The Architecture of the Galaxy
Learning Objectives By the end of this section, you will be able to: The Milky Way Galaxy surrounds us, and you might think it is easy to study because it is so close. However, the very fact that we are embedded within…
Thinking Ahead
Figure 25.1 Milky Way Galaxy. The Milky Way rises over Square Tower, an ancestral pueblo building at Hovenweep National Monument in Utah. Many stars and dark clouds of dust combine to make a spectacular celestial sight of our home Galaxy. The location has…
Summary
Introducing General Relativity Einstein proposed the equivalence principle as the foundation of the general theory of relativity. According to this principle, there is no way that anyone or any experiment in a sealed environment can distinguish between free fall and…
Gravitational Wave Astronomy
Learning Objectives By the end of this section, you will be able to: Another part of Einstein’s ideas about gravity can be tested as a way of checking the theory that underlies black holes. According to general relativity, the geometry…
Evidence for Black Holes
Learning Objectives By the end of this section, you will be able to: Theory tells us what black holes are like. But do they actually exist? And how do we go about looking for something that is many light years…
Black Holes
Learning Objectives By the end of this section, you will be able to: Let’s now apply what we have learned about gravity and spacetime curvature to the issue we started with: the collapsing core in a very massive star. We…
Time in General Relativity
Learning Objectives By the end of this section, you will be able to: General relativity theory makes various predictions about the behavior of space and time. One of these predictions, put in everyday terms, is that the stronger the gravity, the…
Tests of General Relativity
Learning Objectives By the end of this section, you will be able to: What Einstein proposed was nothing less than a major revolution in our understanding of space and time. It was a new theory of gravity, in which mass determines the…