BIG HISTORY – UNIT FIVE
How were stars formed?
David Christian explains how the first stars were formed. This two-part lecture begins by focusing on what
the Universe was like in its first 200 million years of its existence, a period in which there were no stars. It
then takes up the process of star formation. Gravity is the key player in this part of the story, and gravity will
also be critical to the formation of larger, more complex structures in the Universe such as galaxies, clusters,
and superclusters. The cosmic background radiation, which provided important evidence for the story of the
Big Bang in Unit 4, is also important here, providing evidence about the conditions that led to star formation.
After reading the text below and watching the video, you should be able to explain the process of star
formation and why star formation counts as the second major threshold in the story of Big History.
PART 1
0:00 – 2:02
What was the Universe like before the first stars formed?
What evidence does the cosmic background radiation provide about the Universe during its Dark
Age?
Before the first stars formed, the universe was cold and dark and growing colder and darker, this
was called the “dark age.” Here, Atoms flowed through space and the cosmic background radiation
shoed that matter was distributed extremely equally throughout the universe; temperature, density,
types of atoms, really everything was uniform.
2:03-2:47
How were Goldilocks Conditions defined in Unit 1?
What Goldilocks Conditions were necessary for the formation of stars?
Goldilocks conditions were defined as conditions that needed to be met to make a threshold or an
event occur; more simply, they were the circumstances that needed to be perfect for something to
happen. In order to form the stars, the goldilocks conditions were “lots of matter, gravity, and tiny
differences in the distributions of that matter.”
2:48—3:22
What does the cosmic background radiation tell us about early star formation?”
It showed us that there were tiny fractions of differences in the temperature of the cosmic
background radiation (1/1000th of a degree) so gravity could magnify those differences and create
stars.
3:23—4:41
What were the characteristics of gravity that you learned in Unit 4?
Is it fair to call the clumping of matter that takes place in star formation a “runaway train”? Why or
why not?
As we learned in Unit 4, gravity is one of the four fundamental forces where it defines how things
are attracted to one another (i.e. things denser have a larger gravitational pull and as you move
away, that pull is weaker). It is fair to call the clumping of matter that takes place in star formation a
“runaway train” because it is a cycle that says when a clump of matter is dense, it attracts more
matter and becomes even more dense, attracting more matter and becoming denser yet, and so on.
It is a cycle that could never end.
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PART 2
0:00—1:13
What conditions get the process of star formation started?
The collision of particles heats up the matter clump, which at 3000 degrees breaks atoms apart and
then finally at 10 million degrees protons fuse together through nuclear fission and create a pure
energy release, creating a star.
1:14—2:10
Why does the “runaway train” finally stop rather than go on forever?
The runaway train finally stops rather than going on forever because as the temperature rises from
the clumping of more matter and that matter colliding with each other, it gets so hot that nuclear
fission occurs and protons create energy instead of being matter.
2:11—3:22
Complex things have diverse ingredients, a precise arrangement, and emergent properties. How do
stars exhibit the characteristics of complex things?
Diverse Ingredients – stars are made up of many chemical elements, mostly hydrogen and helium
though, but all matter can come together and fuse to become a star
Precise Arrangement – Stars have a defined system and model where protons are constantly
sinking down to the core of the star where they will fuse and release energy. Also, photons of
energy are constantly seeking their way out of the core through the star
Emergent Properties – stars emit energy in all forms especially light and heat
3:23—4:29
Gravity can create galaxies, clusters, and superclusters, but it can’t create structures larger than
superclusters. Why is there a limit to the creation of even larger complex structures in the Universe?
Gravity cannot create larger structures than super clusters because after that, gravity becomes too
weak to hold anything larger together.
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