![]() These are stars that have exhausted hydrogen in their centers, and have swelled up to become red giants. ![]() Note that it contains several orange-color stars. (b) This ground-based photograph shows the open cluster M41. Some of its more massive stars are no longer close to the zero-age main sequence (red line). (a) Cluster M41 is older than NGC 2264 (see Figure 22.10) and contains several red giants. ![]() We see a gap for M41 because at this particular moment, we have not caught a star in the process of scurrying across this part of the diagram.įigure 22.12 Cluster M41. In this case, it simply represents a domain of temperature and luminosity through which stars evolve very quickly. A gap does not necessarily imply that stars avoid a region of certain temperatures and luminosities. Note the gap that appears in this H–R diagram between the stars near the main sequence and the red giants. Beccari)įigure 22.12 shows the H–R diagram of the open cluster M41, which is roughly 100 million years old by this time, a significant number of stars have moved off to the right and become red giants. The bright orange star in NGC 3293 is the member of the cluster that has evolved most rapidly. The most massive stars, however, exhaust their nuclear fuel more rapidly and hence evolve more quickly than stars of low mass. All the stars in an open star cluster like NGC 3293 form at about the same time. Kippenhahn and his associates at Munich University for a hypothetical cluster with an age of 3 million years.įigure 22. These ideas are illustrated in Figure 22.8, which shows the H–R diagram calculated by R. After a few million years (“recently” for astronomers), the most massive stars should have completed their contraction phase and be on the main sequence, while the less massive ones should be off to the right, still on their way to the main sequence. What does theory predict for the H–R diagram of a cluster whose stars have recently condensed from an interstellar cloud? Remember that at every stage of evolution, massive stars evolve more quickly than their lower-mass counterparts. ![]() The key observation is that the stars in these different types of clusters are found in different places in the H–R diagram, and we can use their locations in the diagram in combination with theoretical calculations to estimate how long they have lived. In this section, we will show how we determine the ages of these star clusters. In the previous section, we indicated that open clusters are younger than globular clusters, and associations are typically even younger. Describe how the main-sequence turnoff of a cluster reveals its age.Explain how the H–R diagram of a star cluster can be related to the cluster’s age and the stages of evolution of its stellar members.By the end of this section, you will be able to: ![]()
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