Life Cycles of High and Low Mass Stars
Topic/Concept: Stellar Evolution
Type of Activity: small group + discussion at the end
Prerequisite knowledge required: hydrostatic equilibrium (gravity vs pressure), nuclear fusion, ideal gas law
Resources required: image packets (see below)
Learning Objectives: order the images to represent the correct procession of stages in the life of a star (for the high mass and low mass cases), describe what is happening in each stage and between stages
Common misconceptions:
Detailed description of activity: i put the students in small groups and give each group a packet of images. i remind them how we recently talked about hydrostatic equilibrium and how stars spend their lives balancing against gravitational collapse. then i set them free to order the images and write down as much detail as they can about each image and the transitions between them. i leave time at the end to go over the correct order on the board, having the students present their order and throw out details. the instructor can then add anything they missed or clarify details.
Assessment: this is mostly done through interacting with the students as they work in groups and present information at the end of the class. you could ask them to write up the life cycle of a star (for the high and low mass cases) and turn that in.
Associated files and images: (LM=low mass, HM=high mass) LM1 – molecular cloud, LM2 – main sequence star, LM3 – H shell burn, He core inert, LM4 – H shell burn, He core burn, LM5 – H shell burn, He shell burn, inert C core, LM6 – planetary nebula (M57), LM7 – white dwarf, HM1 – molecular cloud, HM2 – main sequence,HM3 – onion, HM4 – SN1987a before and after
Comments: the intention for this activity is that the students have never had stellar evolution taught to them but they do know what a star is and that it wants to be in equilibrium and that gravitational energy cannot be the only power source. (hopefully they’ve seen a calculation of the kelvin-helmholtz timescale in the previous lecture.) so during this activity they use their knowledge of hydrostatic equilibrium, the ideal gas, law, and fusion to figure out what happens to a star throughout its lifetime.
the images are from a bunch of random sources and i wish they were more standardized.
This worked great with our COSMOS kids! I kept telling Emily that they were going to finish it in 5 minutes and be all slack about it, but it really caught their imaginations. (In the end, just doing the high mass star took approx. 1 hour—keep in mind, these are smart high school kids) They wrote up really nice summaries in the end, about what they thought was happening in each stage. It was a little harder to get them thinking about what happens between stages—we really had to lead them to the ‘core shrinks and gets hotter until the next element can fuse’ part.
We did the high mass star in detail, and I think maybe the only problem was that going from main sequence to the onion star skips over so many steps. Perhaps they would have thought more about the transformations between stages if they hadn’t been so overwhelmed by that crazy multi-layer star. We should try to find/make pictures of intermediate stages.
But all in all, this project really got them thinking! The deepest understanding of stellar evolution my students have ever had! Much better than lecture! Laura Chomiuk | 5 August, 10:37 PM | #