1. Goal: To understand clusters of stars Objectives: 1)To explore Some nearby clusters 2)To understand How clusters in our galaxy form 3)To understand Globular clusters 4)To learn about What we can determine from clusters 5)To explore the Local region

2. Nearby clusters Here are the Hyades and Pleiades clusters. These are two of the closest star clusters to us. Which one do you think is closer? Top group is Pleiades, bottom is Hyades.

3. Nearby clusters These are called open clusters (because they are not tightly bound and will eventually drift apart). Open clusters are young (usually < 1 billion years old).

4. Another cluster This is the Urza Major moving cluster. Moving clusters are sets of stars that all move in the same direction. This means they all came from the same place. Age ~ 800 million years

5. Another cluster This cluster is passing us currently. We are just on its outskirts. However we are definitely NOT a member of this cluster. How can we tell?

6. Another cluster How can we tell? Well, our sun is 4.5 billion years old. And the cluster is moving by us at 46 km/s. 46 km/s = 1 light year per 6000 years

7. A bit further out… Beehive Cluster (M44) 577 light years Also about 800 million years old

8. So, basically… Open clusters are YOUNG clusters that drift apart in about a billion years. As viewed from Earth you tend to see the blue high mass stars. Those are always young stars as they don’t last long. These are clusters with stars of equal age, distance, and composition, but range in mass.

9. In our galaxy alone We know of over 1000 of these types of clusters. However, there are probably far more – maybe even 100,000. What happens to the lower mass stars of the cluster after a billion years?

10. Globular Clusters What is different about this cluster?

11. Omega Centauri Brightest globular cluster. Millions of stars closely packed. This is a closed group. Close or far away?

12. Omega Centauri The diameter is only 150 light years. Brightest globular cluster. It is 15000 light years away!

13. Globular Cluster 47 Tucanae 2 nd brightest. There are about 150 known globular clusters for our galaxy. I say for not in because they all are on the outskirts of our galaxy (sort of like suburbs). Notice the cluster looks very red – what does that tell you about this cluster?

14. NGC 6723 Where is it on this image? NGC 6723 is 30,000 light years away vs 500 light years for the dark spots.

15. M15 – from HW4

16. Why are clusters important? What can we learn by studying a cluster?

17. Why are clusters important? What can we learn by studying a cluster? Age of cluster Distance to cluster A key step in finding distances to other galaxies. How stars evolve How clusters evolve How our galaxy evolves How the composition of our galaxy changes with time How stars and clusters are formed

18. 400 light years

19. 1500 Light Years

21. Conclusion Clusters are very useful and important. All stars star in clusters. Open clusters are young clusters in the disk of our galaxy which only stay for about a billion years. Globular clusters are old and lie on the outskirts of our galaxy.