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Chapter 3

NATS 1880 Chapter Notes - Chapter 3: Radiant Energy, Molecular Cloud, University Of Manchester

Natural Science
Course Code
NATS 1880
Richard Gasparini

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The Universal Context of Life
Begins where Newton left off
Three important ideas in framing the universal context
oThe universe is vast and old
Great potential for life, old age implies time for it to begin and
oThe elements of life are widespread
Basic chemical elements that make up Earth and life are
present throughout the universe
oThe same physical laws that operate on Earth operate throughout the
Newton’s conclusion that the laws of nature are the same
everywhere is supported by tests; reasonable to think that the
same processes are possible on other worlds
These ideas reinforce the Copernican revolution: WE ARE NOT THE CENTER
oPlanet in our solar system
oSolar system in our galaxy, Milky Way
oOur galaxy in Local Group
oThe Local Group is in the Local Super-cluster
oAll a part of the universe
Light year (ly) is the distance a photon of light will travel in a year
o9.46 x 10^12km
Alpha Centauri
oOur closest star system, would take us 4.3 ly to get to aka at 50,000
km/h it would take 100,000 years
Orion Nebula (M42)
o1500 ly away, thus we are seeing the nebula as it was 1500 years ago
Our Galaxy - Milky Way
100,000 ly across and home to about 200 billion stars and dark matter
The more massive the galaxy, the stronger its gravity and the faster stars
should be orbiting
oBy studying stellar orbits, astronomers have put together a map of the
distribution of matter in the Milky Way
The Universe Contains
All of the matter and energy in existence
Planet, stars, etc. (baryonic matter): 4%
Dark matter (28%)
Dark energy or vacuum energy (68%)

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oPushing galaxies apart even while their gravity tries to draw them
oMeans its gravity played a key role in assembling galaxies
oEvidence has been building for decades
These are the main ingredients of the universe
Do not affect general evolution, do not affect study of other life
Birth of universe
oBig Bang
Galaxies as cosmic recycling plants
oEarly universe contained only hydrogen and helium
oOther elements were made by stars and recycled within galaxies
Life Cycle of Stars
oBorn in clouds of gas and dust, explode when they die
Earth and Life
o4.5 billion years ago, 2% of the original elements converted to heavier
Big Bang and the Expanding Universe
Telescopic observations reveal the entire universe is expanding; average
distances between galaxies are increasing with time
oNote: individual galaxies and clusters do not expand
oImplies galaxies were closer together, beginning of the expansion is
the Big Bang 13.8 billion years ago
oDetected radiation left over from B.B.
Universe was hotter and denser if it was smaller, producing
radiation (light)
Should have left behind a faint glow, known as cosmic
microwave background
oOverall chemical composition of the universe
If the B.B. occurred, it should be ¾ hydrogen and ¼ helium
Stellar Lives and Galactic Recycling
Stars are born when gravity compresses the material in a cloud until the
center is dense enough and hot enough to generate energy by nuclear fusion
oProcess of lightweight atomic nuclei smashing together, fuse to make
heavier nuclei
oSome mass lost will become energy (E = m x c^2)
Massive stars die in explosions called supernovae and returned matter mixes
to form new stars
oEx. The Crab Nebula
Evidence we’re made of stars:
oYounger stars (sun) were born with higher proportions of heavy
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