Download This chapter has a brief overview of astronomical topics that we will

Chapter 33
Astrophysics and Cosmology
This chapter has a brief overview of astronomical topics (read 33-2). Stars are born from large
clouds of gas and dust. A disturbance causes the cloud to collapse and fragment into many protostars. The life of a star depends on its mass (and to a lesser extent, chemical composition).
A star like the sun will fuse hydrogen into helium in its core and remain stable for billions of
years. A more massive star lives a hotter, shorter life. In a few billion years the core of the sun
will contract and the outer layers expand. It will expand almost to the orbit of the earth, ending
all life on our planet. This is the red giant phase (the outer layers cool as the great size
overmatches increased energy production). Eventually, the outer layers are blown away and the
sun will be a white dwarf the size of the earth, generating no energy but cooling very slowly.
More massive stars can fuse other elements and develop multiple layers burning different nuclear
fuels. These stars do not end as white dwarfs but as more massive neutron stars or black holes.
Let's examine the origin of the universe (read 33-4 to 33-7).
The standard model of cosmology holds the universe began 10 to 12 billion years ago. We do
not understand the moment of creation, but current physics can extrapolate back to a tiny fraction
of a second after this event. All of space and time was created in this "Big Bang". There was
nothing before (as there was no time) and it was not an explosion in space (since space was
created here). Why do we believe this?
We see the galaxies flying apart from each other, the farthest moving faster. Since we see the
more distant galaxies as they were long ago, this seems to imply an explosive creation at a time
when all the galaxies were crowded close together long ago.
We can calculate how the Big Bang and later stars would evolve and produce nuclear elements
heavier than hydrogen. The observed abundances agree with our ideas about the origin of the
elements and the state of the universe long ago.
The creation involved enormous energies heating the early cosmos with γ -rays. As space
expanded this radiation was stretched (cooled) until now it would be mere microwave static.
Penzias and Wilson observed this microwave background radiation in the 1960's. The snow or
static you see on unused (non-cable) VHF TV channels is partly this remnant of creation. The
spectrum of this radiation follows the curve of a blackbody cooled to 3K, as predicted by the Big
Bang theory.
This is still a field of active research, and we have much yet to learn. Recent work into missing
mass, dark matter and the cosmological constant suggest how far we have to go.
We started this course finding the velocity of penguins slipping on ice and end it contemplating
the creation of space and time. Where will we go from here?