Book contents
- Frontmatter
- Contents
- Preface
- Background: what you need to know before you start
- 1 Gravity on Earth:
- 2 And then came Newton
- 3 Satellites
- 4 The Solar System
- 5 Tides and tidal forces
- 6 Interplanetary travel
- 7 Atmospheres
- 8 Gravity in the Sun
- 9 Reaching for the stars
- 10 The colors of stars
- 11 Stars at work
- 12 Birth to death
- 13 Binary stars
- 14 Galaxies
- 15 Physics at speed
- 16 Relating to Einstein
- 17 Spacetime geometry
- 18 Einstein's gravity
- 19 Einstein's recipe
- 20 Neutron stars
- 21 Black holes
- 22 Gravitational waves
- 23 Gravitational lenses
- 24 Cosmology
- 25 The Big Bang
- 26 Einstein's Universe
- 27 Ask the Universe
- Appendix: values of useful constants
- Glossary
- Index
14 - Galaxies
Atoms in the Universe
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- Preface
- Background: what you need to know before you start
- 1 Gravity on Earth:
- 2 And then came Newton
- 3 Satellites
- 4 The Solar System
- 5 Tides and tidal forces
- 6 Interplanetary travel
- 7 Atmospheres
- 8 Gravity in the Sun
- 9 Reaching for the stars
- 10 The colors of stars
- 11 Stars at work
- 12 Birth to death
- 13 Binary stars
- 14 Galaxies
- 15 Physics at speed
- 16 Relating to Einstein
- 17 Spacetime geometry
- 18 Einstein's gravity
- 19 Einstein's recipe
- 20 Neutron stars
- 21 Black holes
- 22 Gravitational waves
- 23 Gravitational lenses
- 24 Cosmology
- 25 The Big Bang
- 26 Einstein's Universe
- 27 Ask the Universe
- Appendix: values of useful constants
- Glossary
- Index
Summary
We are now ready to make another step outwards in our exploration of the Universe: we change from looking at stars to looking at galaxies. As we saw in Chapter 9, galaxies are vast collections of stars. Our own Galaxy, the familiar Milky Way, contains about 1011 stars. Figure 14.1 on the following page shows photographs of two typical galaxies. Galaxies are held together by the mutual gravitational attraction of all the stars. It is remarkable indeed that Newton's force of gravity, which he devised in order to explain what held the planets in their orbits, turns out to explain just as well what holds the whole Milky Way together.
In this chapter: we finally reach the basic building blocks of the Universe: galaxies. Galaxies come in many shapes and sizes. They foster the formation of stars and harbor giant black holes in their centers. They contain only some of the mass in the Universe: much more is dark and unidentified. As beacons of light, they allow astronomers to measure how rapidly the Universe is expanding. Their first stages of formation are imprinted on the cosmic microwave background radiation.
Galaxies are more than just collections of stars. The collective gravity of all the stars makes the centers of galaxies very unusual places. Stars and gas crowd together so densely that in some cases they can form immense black holes, with masses of millions or even billions of stars.
- Type
- Chapter
- Information
- Gravity from the Ground UpAn Introductory Guide to Gravity and General Relativity, pp. 163 - 178Publisher: Cambridge University PressPrint publication year: 2003