Using Hubble Types to Understand Galaxy Evolution
Topic/Concept: Hubble Diagram and Galaxy Evolution
Type of Activity: Group activity
Prerequisite knowledge required: Hubble Diagram
Resources required: Pictures of different types of galaxies might be helpful. There’s nice big Hubble Atlas in the Library.
Learning Objectives: Gain a greater understanding of the scientific method.
Common misconceptions:
Detailed description of activity:
The Hubble types were explained in lecture, so I simply summarized the differences again. I then asked what the use of these classifications were. I steered the class towards the assumption that galaxies of the same Hubble type were similar in other respects. I then wrote on the board a summary of numerical differences between elliptical and spiral galaxies (i.e. linear size, color, mass, shape, star population type, normal orbit formation, etc…). At this point I broke the class into groups of about 4 and asked them to come up with an explanation of the evolution of galaxies. I started them out with a few fundamental questions like: Which came first, spirals or ellipticals? Do spirals evolve into ellipticals or the other way around or neither? etc…
In the last five minutes, I explained the idea of spirals merging and forming ellipticals. If I was really prepared, I had a slide ready of two spirals actually colliding. I then asked the class if they would expect anything else to be true if this evolutionary process actually occurred. I steered them toward the idea of spirals being more common in the past. I presented this as a prediction of the theory which could actually be tested quantitatively. This topic really gives us a chance to talk about what it means to do science and why prediction plays such a central role in the field.
Assessment:
Associated files and images: None.
Comments: I emphasized that even though they didn’t have the evidence in front of them to definitively answer the evolution question, they could at least come up with a self-consistent picture. Any explanation should at least predict the qualitative differences in color, mass etc. between spirals and ellipticals. This project is a bit risky because some students can rebel at the idea that there isn’t necessarily one definitely correct answer. I have to admit to liking this project, however, because I think, with care, it can help people get an idea of how scientific ideas are evaluated.
By Christer Watson (8/99)