Figure 23.1 Stellar Life Cycle. This remarkable picture of NGC 3603, a nebula in the Milky Way Galaxy, was taken with the Hubble Space Telescope. This image illustrates the life cycle of stars. In the bottom half of the image, we see clouds…
Evolution from the Main Sequence to Red Giants When stars first begin to fuse hydrogen to helium, they lie on the zero-age main sequence. The amount of time a star spends in the main-sequence stage depends on its mass. More…
Learning Objectives By the end of this section, you will be able to: If what we have described so far were the whole story of the evolution of stars and elements, we would have a big problem on our hands.…
Learning Objectives By the end of this section, you will be able to: The “life story” we have related so far applies to almost all stars: each starts as a contracting protostar, then lives most of its life as a…
Learning Objectives By the end of this section, you will be able to: In the previous section, we indicated that open clusters are younger than globular clusters, and associations are typically even younger. In this section, we will show how…
Learning Objectives By the end of this section, you will be able to: One of the best ways to get a “snapshot” of a group of stars is by plotting their properties on an H–R diagram. We have already used the…
Figure 22.1 Ant Nebula. During the later phases of stellar evolution, stars expel some of their mass, which returns to the interstellar medium to form new stars. This Hubble Space Telescope image shows a star losing mass. Known as Menzel 3, or the Ant…
Star Formation Most stars form in giant molecular clouds with masses as large as 3 × 106 solar masses. The most well-studied molecular cloud is Orion, where star formation is currently taking place. Molecular clouds typically contain regions of higher density…
Learning Objectives By the end of this section, you will be able to: Traditionally, astronomers have assumed that the planets in our solar system formed at about their current distances from the Sun and have remained there ever since. The…
Learning Objectives By the end of this section, you will be able to: Before the discovery of exoplanets, most astronomers expected that other planetary systems would be much like our own—planets following roughly circular orbits, with the most massive planets…