Slides: Raided the Departmental collection to get
Other things to dig up (besides projectors):
So, we designed a new lesson plan for explaining this. It's totally new, so we need their help to learn how to improve it.
Talk about our KWL. (not worth the time of making into overhead, although that's waht I originally intended.) (This document has big fonts because it's essentially ready to be turned into an overhead.)
Boy, I hope they know decimals. Evidence suggests this is a 6th grade thing? They did know decimals.
We need to define mass - first ask them what they think mass is. Some of them knew, but got the idea across, i think.
We need to define notation Mo, since I'm not going to write out "solar masses" every time I need to. :-)
We need to find out who is going to be what star, but first we need to find out what kinds of stars we need.
State that most of the stars in the Galaxy (and the Universe) are stars like the Sun and lighter. Use graph of our Initial Mass Function (IMF) and compare to Salpeter IMF. Talk about what it means. Graph will be number of stars versus mass, so I can ask, "How many lightweight stars do we need?" (lots) and "How many heavy stars do we need?" (not very many) Need to fix our IMF to match Salpeter a little better. (fewer 5 Mo's for example.)
Put kids in circle -- move furniture, etc, so that they can stand in circle and see screen at same time. Display stars overhead and talk through it. "What makes a star a star?" What defines the difference between just a cloud of gas and a star? Take answers; I expect, "it glows." What makes it glow? Nuclear energy generation. Talk through imaginary picture of star collapses, and in doing so heats up. We all know that hot things expand, so the collapse is pretty slow, since it's battling the expansion due to temperature. Finally, the center reaches the point where we can turn H into He, so now the temperature skyrockets. pressure out = pressure in
grab several of the kids destined to be low-mass stars and do the pressure out = pressure in demo. 4 kids in inside, face to face with 4 kids outside. kids on inside are pushing out with gas pressure, kids on outside are pushing in with gravitational pressure.
NOW...
Assign kids to stars.
This is the distribution we're working towards: Way to read this table is "4 kids make up 1 star representing a 15 Mo star" all the way down to "8 kids make up 16 stars representing 0.8-1 Mo stars." There are 45 kids used here; if we have more than 45 kids, put them in the low-mass end, and make sure we have enough gumdrops (see below).
| No. kids | No. stars | Mass (Mo) |
| 4 | 1 | 15 |
| 3 | 1 | 10 |
| 4 | 2 | 9 |
| 5 | 5 | 5 |
| 6 | 6 | 3 |
| 7 | 7 | 2 |
| 8 | 8 | 1 |
| 8 | 16 | 0.8-1 |
Make index cards that say things like "you are part of a 15 solar mass star" etc. (see below.) These should be tied to a baggie that contains, at minimum, 4 gumdrops, toothpicks, and a paper towel/napkin. MAKE SURE THEY KNOW NOT TO OPEN THE BAGGIE YET!
| Mass (Mo) | Contents of bag and other notes |
| 15 | *each* kid in star, all 4, gets a bag with 4 gumdrops, etc.
card says: You are part of a 15 Mo star, the most massive star in our cluster. There should be 3 others who are also part of this star. All of you together will end up as a black hole. |
| 10 | *each* kid in star, all 3, gets a bag with 4 gumdrops, etc.
card says: You are part of a 10 Mo star, the second-most massive star in our cluster. There should be 2 others who are also part of this star. One of you will end up as a neutron star, but the rest of you will end up as a nebula -- "star guts" spread out all over the place. |
| 9 | both kids in both stars get their own bag with 4 gumdrops, etc.
The partners here should be good friends, because they'll need
to get close together.
card says: You are half of a 9 Mo star. There are two of these kinds of stars in our cluster, but you are half of just one of them. You will end up as a neutron star. |
| 5 | Each kid is a star here, and there are 5 of them. Each kid gets a bag.
card says: You are a 5 Mo star. You get to be a star all by yourself, so you don't have any partners, but there are 4 other stars like you in the cluster. You will end up as a neutron star. |
| 3 | Each kid is a star here, and there are 6 of them. Each kid gets a bag.
card says: You are a 3 Mo star. You get to be a star all by yourself, so you don't have any partners, but there are 5 other stars like you in the cluster. You're going to need your coat, but don't go get it yet. We'll tell you when you can go. You are going to end up as a white dwarf. |
| 2 | Each kid is a star here, and there are 7 of them. Each kid gets a bag.
card says: You are a 2 Mo star. You get to be a star all by yourself, so you don't have any partners, but there are 6 other stars like you in the cluster. You're going to need your coat, but don't go get it yet. We'll tell you when you can go. You are going to end up as a white dwarf. |
| 1 | Each kid is a star here, and there are 8 of them. Each kid gets a bag.
card says: You are a 1 Mo star, a star just like our own Sun. You get to be a star all by yourself, so you don't have any partners, but there are 7 other stars like you in the cluster. You are going to end up as a white dwarf. |
| 0.8 | Each kid is TWO stars here. There are 16 stars, so 8 kids. Each star
gets a bag, so each kid gets two bags. Card says: You are a 0.8 Mo star, a star lighter than our own Sun. There are a LOT of your kinds of stars in our Galaxy, so actually you get to be TWO stars at once, so you get a bag of gumdrops for each star you are, two bags. There are 7 other kids who are also being 2 stars in the cluster. It's going to take you more than the age of the Universe to finish turning all your hydrogen into helium. |
Let the chaos of distributing bags settle a little, and set up posters appropriately. Send the 3 and 2 Mo kids off to get their coats. They shouldn't put on their coats yet.
Call their attention again to Orion nebula slide. Run through more pictures of star forming regions, even if it's just more of Orion.
Tell them that their classroom is now interstellar space, a giant cloud of gas and dust. It's pretty quiet in this neighborhood of the Galaxy. ..Until something happens to start forming stars.
Point out that the most massive stars in reality have the most "stuff to work with" -- and those stars in our cluster have the most gumdrops. (Explain that gumdrops represent H.)
So, now, the stars in our cluster have all condensed and are about to start burning hydrogen.
let them go and do this on their own.
Regain control of the class and tell them that nothing really happens in the cluster for about 100 thousand years. Nothing happens yet.
Talk about how the most massive stars are the hottest and biggest, and ask each group what color they think they are and what size they think they are.
The heaviest stars are also the hottest, so this means the insides are the hottest, so it means they're turning H->He the fastest. As they run out of fuel, the pressure out changes, so what do you think will happen?
Organize the kids with one person in the center, and three kids holding hands around the center person. As the pressure goes away, first the core contracts, then it heats up, then it starts to turn He into other things (carbon). The 3 kids on the outside back up to be even bigger than they were before, make them be as big as they can be.
These kids started with 4*4 hydrogens, now have only 4 heliums, so things are going to go faster now, like 10 thousand years to run out of He. Even on these timescales, it only takes about a month for the heaviest one to go through C, a week for Ne, then a day for Si -> Fe.
Specifics on burning products from Clayton:
H->He4, He3 from incomplete PP chain
DLiBeB bypassed. production from non-thermal processes.
He->C12, O16, O18, Ne22 from alpha captures by N14 during
3alpha process.
N14 from CNO in process of H burning, also some C13, N15, O17.
Ne20, Na, Mg, Al, Si28 partly due to C burning
Mg, Al, Si, P, S partly due to O burning.
4H->4He 3He4->C12 2C12->Mg24 2O16->S32
THEN, we tell the kid in the center he (or she) is now iron, and she or
he squats down and gets small and THEN the outer layers get to fall in
and join that kid in an alternate universe as (s)he becomes a black
hole. The kids get to eat their gumdrops and watch the rest of the
drama.Overhead for process of h, run out of fuel, he, ... ?
Again, as before, through the giant stage, repeat what we said about fuel expenditure. This time, though, the outer layers get to then bounce off and run away. We bring a basketball and tennis ball to do "that demo" about the outer layers bouncing off. The kid in the center is now a neutron star and the rest of the kids are stuff like the crab nebula (and show poster). If we want, we can have the kid in the center spin until she gets sick to demonstrate pulsars. Mention how a spinning ice skater goes faster when she pulls in her arms.
We should also mention that this is how the Galaxy gets enriched with all the CNO that make up us.
These kids eat their gumdrops and watch the rest. They are heavier than the Sun, but the size of Chicago.
These kids become neutron stars and eat their gumdrops. They are about the mass of the Sun, but the size of Chicago.
Then, talk about how, this time, when it runs out of fuel, it starts to collapse, and thus heats up. But, this time, it gets hot enough to expand back again before it can burn the next stage. Then it collapses again, heats up, and expands again, each time losing a little bit of mass.
Let them "pulse" and throw off their outer layers.
Show slides and talk about what happened again.
These kids are now white dwarfs, about the size of the Earth and the mass of the Sun. They eat their gumdrops.
They become WDs, a little lighter than our Sun, but about the size of the Earth.
These kids (finally) get to eat their gumdrops.