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Journal 2/28/17
Which stage in the life of a star is your favorite? Why
Objective
Tonight’s Homework
To fill out our understanding of
the life stages of a star
p 488: review 1-4, 6, 7
Finishing Our Poster
Let’s start class by putting together all the items on our
poster.
Once the poster is complete, take the first 20 minutes of
class to get notes on the stages. We’ll add a bit more to
this in “official” notes later, but this poster will be your
main source of notes for this topic!
Extra Notes on Stellar Evolution
Molecular Clouds – Hundreds of light years
across, can contain enough material to make
millions of stars.
This cloud is
usually spinning
VERY slowly
in some direction.
Extra Notes on Stellar Evolution
This bump here is the
size of the solar system
Extra Notes on Stellar Evolution
As the Protostar collapses, fusion starts in the
middle and everything speeds up in which way it
was spinning. This is why everything in a star
system orbits and spins in the same direction.
Extra Notes on Stellar Evolution
Actual Protostars
Extra Notes on Stellar Evolution
After our protostar settles down a bit, we
classify it as a main-sequence star. The star will
now stay stable for 90% of the rest of its life,
happily burning hydrogen into helium.
But we still have a huge ring of dust and gasses
going around our star. What happens to that?
This gas and dust will start colliding and
clumping to form planets.
Extra Notes on Stellar Evolution
This gas and dust starts clumping into balls
hundreds or thousands of miles across. After a
while, we have clumps about half the size of the
moon called “planetesimals”.
Extra Notes on Stellar Evolution
As the planetesimals clump and collide,
eventually a handful of big ones start to
dominate and collect more and more stuff. By
the time this process is nearly over, we have
maybe a 15-20 planets in a system, all
completely
molten and
still being
hit by asteroids
all the time.
Extra Notes on Stellar Evolution
However, this gives us too many planets for
orbits to be stable. As things settle down, we’ll
occasionally have two large planetesimals
(almost planet sized) collide and merge. We
think this happened to the Earth a long time ago
and that’s
what formed
the moon.
Extra Notes on Stellar Evolution
After all this is done, we finally have a finished
star system. Collisions and asteroids will still
exist, but things are stable now and big
collisions are fairly rare.
Now our star and planets are at the Main
Sequence stage!
Exit Question
What is a planetesimal?
Something that looks like a planet but isn’t.
What we call a planet after it dies
The name of a galactic superhero
What we call big chunks of rock that form into planets
None of the above