Sloan Digital Sky Survey SkyServer DR15

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# Conclusion

You now know a great deal about what galaxies are, what they look like, and how they affect one another. But you can also study one more question: how do galaxies evolve through time? Hubble tried to solve this problem: he thought that galaxies evolved to the right on the tuning fork diagram. He was mistaken. Do you think you can figure out the answer to the problem that stumped Hubble?

# Galaxy Evolution

This section will take a lot of time and effort, but it gives you the opportunity to solve the problem that Hubble couldn't solve! The Research Challenge below will guide you through your study. Do this section on your own, and take your time. Have fun with it. When you finish, E-mail us your diagrams and an explanation of what you found, We'll look at all the results we receive, and we'll put the best work up on this site!

The galaxy cluster you looked at in this project, Abell 2255, is at redshift 0.081. By looking at different redshifts, you look at different distances away from Earth (see the Hubble diagram project for more information). Because the speed of light is finite, when you look at larger distances, you are looking at things as they were in the more distant past. So by looking at galaxy clusters of different redshifts, you can see if galaxies have evolved over time.

One easy way to tell if galaxies have changed is to see if their colors have changed. The Research Challenge guides you in making a color-color diagram of galaxies at different redshifts. Can you think of other ways to study galaxy evolution?

Research Challenge. Make color-color diagrams for galaxies at a variety of redshifts. Look at the percentage of early and late galaxies as a function of redshift. Are there more spirals now than there were in the past? Or are the more ellipticals now than in the past? The table below lists some galaxy clusters and their redshifts. Can you see the colors change due to the redshift?

 Cluster Name Redshift Abell 0023 0.105 Abell 0102 0.0635 Abell 0119 0.044 Abell 0189 0.0328 Abell 0267 0.230 Abell 0370 0.375 Abell 0381 0.1794 Abell 0919 0.0954 Abell 0194 0.0180

Search for these clusters using whatever tools you find useful. Large astronomical databases like NED and SIMBAD will help you find some information on these clusters. You can enter their names into NED or SIMBAD to find their positions in the sky. Some clusters have SDSS data, but for some, you will have to look at other online data sources like the Chandra X-Ray Observatory.

After you get your images and data, you will need to eliminate foreground and background galaxies to get a true look at galaxies in the cluster. The redshifts listed above will help you with this.

This is a tough research challenge, and it would make a good choice for a project for Science Fair or Intel Science Talent Search. Good luck!

Project designed by Robert Sparks

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