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!
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