Transcript The Universe

What is Science?
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A process to explain the natural world
Science is a truth-seeking process
Certainty is elusive in science
Theory does not mean “guess” or
“hunch“
– A Theory is an explanation of natural
phenomena built up logically from
testable observations and hypotheses
What is Faith?
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Beliefs that are accepted without
empirical (observed) evidence
A few considerations:
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May not be possible to predict all
consequences of an action
Any new finding should be examined
with skepticism
Do not rely on one study
Repeating a false notion does not
make it true
Nonsensical lingo can sound very
scientific
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“Chemical” is not a dirty word
– Di-hydrogen monoxide
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Nature or natural does not mean benign
or safe
Preceived risks are often different from
real risks
Individual foods are not good or bad
If something sounds too good to be
true, it probably is! No short-cuts!
Science is not always correct
Chapter 12
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The Universe
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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“ Can you bind the beautiful Pleiades?
Can you loose the cords of Orion?
Can you bring forth the constellations
in their seasons?
Or lead out the Bear with it’s cubs?
Do you know the laws of the heavens?
Can you set up God’s dominion over
the earth?” Job 38:31-33
The night sky
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Celestial observation dates to ancient civilizations (Job)
• Most ancient Greeks held a Geocentric view of the
universe
 “Earth-centered” view
• Earth was a motionless sphere at the center of the
universe
• Seven heavenly bodies
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Stars
– Appear as point
sources
– Generate their own
light
– Twinkle from
atmospheric
turbulence
– Distance measured in
light years
one ly=9.5x1012 km
9.5 trillion km
5.8 trillion miles
Planets
– Visible by reflected
light
– Extended sources
Keck Telescopes:
the world’s largest optical
and infrared telescopes
Hubble SpaceTelescope
Stars
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Massive, dense balls of
incandescent gas
Powered by fusion
reactions in their core
Sun
Origin of stars
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Gaseous nebula
– Mostly hydrogen
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Shock waves induce
gravitational collapse
– Gravitational energy
released into higher
temperatures and
pressures
– An average star
– Reference for
understanding other stars
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Protostar
– Accumulation of gases
that will become a star
Planetary nebula Aquarius
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Planetary nebulae – are
clouds of ionized gases
No relationship to any
planet
Condense through
gravitational pull to
produce a protostar
Protostars will eventually
become a star
Pillars of Creation Nebula
Ant Nebula
Butterfly Nebula
Crab Nebula
Cat’s Eye Nebula
Horse Head Nebula
Helix Nebula
Heart and Soul Nebula
Witch Head Nebula
Life of a star
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Protostar stage
– Gravitational collapse
– Density, temperature and
pressure increase
– 10 million K: fusion
ignition temperature
– Dynamical equilibrium
 Inward force of gravity
 Outward pressure of
fusion energy
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Main Sequence stage
– More massive stars:
 Higher core, surface
temperatures
 Use up hydrogen more
rapidly
– O type stars
Stellar modeling
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Core
– Very hot, most dense region
– Nuclear fusion releases
gamma and x-ray radiation
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Radiation zone
– Radiation diffuses outward
over millions of years
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Convection zone
– Structured by hot material
rising from the interior,
cooling, and sinking
– Upper reaches: visible
“surface” of star
– Sun surface temp. ~5,800 K
(6,000 C) (11,000 F)
Lifetime of Our Sun
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Converts about 1.4x1017 kg of matter to
energy each year
700 tons of hydrogen into helium each
second
Born 5 billion years ago (give or take)
Enough hydrogen for another 5 billion years
A star’s lifetime depends on it’s stellar mass
– Less massive stars have longer lifetimes
– More massive stars have shorter lifetimes
Sun
Brightness of stars
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Differences in stellar
brightness
1. Amount of light produced by
star
2. Size of star
3. Distance to star
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Apparent magnitude
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What it looks like from earth
Brightness values range from 1
(brightest) to 6 (faintest)
Dim stars have large numbers
Negative numbers are also
used
The more negative, the
brighter it is
Later some stars found to be
brighter than 1
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Sirius -1.42
Sirius
Absolute magnitude
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Brightness adjusted to a defined, standard
distance--all the same distance
Example: Sun
– Apparent magnitude = -26.7
– Absolute magnitude = +5.0
Star Temperatures
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Color variations apparent:
red, yellow, bluish white
Color related to surface
temperature
– Red: cooler stars
– Blue: hotter stars
– Yellow: in between (Sun)
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Classification scheme
– Based on temperature:
hottest to coolest
– O, B, A, F, G, K, M
Star types
Hertzsprung-Russell
diagram
 Plot of absolute
magnitude versus
stellar temperature
 Characteristic grouping
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Main sequence stars
Red giants
Novas
White dwarfs
H-R Diagram
Stellar evolution
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Traces path across HR diagram
1. depletes hydrogen in core
2-3. fuses hydrogen in shell to
become a red giant
3-4 becomes hot enough to
produce helium fusion in the
core
4-5 expands to a red giant as
helium and hydrogen fusion
move out of shells
Eventually becomes unstable
and blows off outer shells to
become a white dwarf
Lifetimes
– O star ~ millions of years
– M star ~ trillions of years
Mass determines ultimate fate
of star
Stellar evolution
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Late red giant stage
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Further core collapse and heating
Helium fusion to carbon initiated
Radius and luminosity decrease,
moves back toward main sequence
The end - less massive
stars
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Helium fuel in core used up;
helium and hydrogen fusion in
shells exhausted
Instabilities blow off outer layers
into a planetary nebula
Carbon core contracts to white
dwarf; cools to black lump of
carbon
The end - massive stars
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More mass: more
gravitational
contraction and
heating
Critical temperature:
600 million K
– Carbon fusion
– Heavier nuclei fuse, up to iron
– All fusion energy sources used
up
– Energy expansion pressure
lost
– Dynamic equilibrium disrupted
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Supernova
– Star collapses and
rebounds from core
– Elements beyond iron
created in explosion and
distributed throughout
Universe
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Subsequent events
depend on mass of
remaining core
End states for massive
stars
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Neutron star
– Remaining core between 1.4
and 3.0 solar masses
– Gravitational pressure fuses
protons and electrons into
neutrons
– Pulsar: rotating, magnetized
neutron star
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Black hole
– Remaining core greater than
3 solar masses
– Gravitational collapse
overwhelms all known forces
– Even light cannot escape the
dense, compact object
Stellar evolution summary
Nova
Supernova
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Crab Nebula
1054
Neutron star
Pulsar
Black hole
Other Star Structures
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Binary systems
– Two gravitationally bound stars
– Most stars are in binary pairs, not
the Sun
Star clusters
– Tens to hundreds of thousands or
more gravitationally bound stars
– Often share a common origin
Binary Systems
Star clusters
Larger Star Structures
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Galaxies
– Basic unit of
the Universe
– Billions and
billions of
gravitationally
bound stars
The Milky Way Galaxy
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Visible as a
diffuse band on a
dark night
Billions of stars,
some bound in
galactic clusters
Other galaxies
Andromeda
 2 million light years away
 Very similar to Milky Way
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Classification scheme (Hubble)
– Elliptical (football), spiral,
barred and irregular
Andromeda
Elliptical Galaxy
Spiral Galaxy
Barred Galaxy
Irregular Galaxy
The life of a galaxy
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Big Bang Theory
Universe evolved
from an explosive
beginning
Supporting evidence
1. Microwave
background
radiation
2. Large scale
expansion
3. Relative abundances
of elements
4. Diffuse cosmic
background
radiation (COBE
spacecraft)
Hubble Deep Field
galaxies