Transcript Document

Homework for today was
WORKBOOK EXERCISE:
“Expansion of the Universe”
(pg. 87-88 in workbook)
Mapping the Universe
Chapter 16
The Local Group
• The Local Group
– group of galaxies
– Milky Way is member
– at least 30 galaxies
• 3 large spirals
– Milky Way,
Andromeda, M33
• remainder mostly
dwarf ellipticals
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Galaxy Clusters
• Most galaxies found in
“galaxy clusters”
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– Examples: Virgo cluster,
Coma cluster
• Superclusters
– extremely rich
galaxy clusters
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Structure in the Universe
• Galaxy surveys show
structure
– voids
– filaments/sheets
• Galaxy clusters
– found within the
filaments/sheets
• Superclusters
– found at intersections of
several filaments/sheets
Evolution of Galaxies
• Galaxy formation
– Universe ~14 billion years
old
– star formation more active
in past
• Galaxies change, as a
result of:
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– star formation
– stellar evolution
– galaxy collisions &
cannibalism
Dark Matter
• Mass of Galaxy Clusters
– determined by galaxy orbital motion
– M/L ~ 300
– Universe is 99% dark matter
The Big Bang
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Chapter 17
Cosmological Principle
• Cosmological principle
– on large scales, Universe is:
• isotropic
– looks the same in all directions
• homogeneous
– any region of space is about the same as any other
Age of the Universe
• Hubble: Universe is expanding
• “Run movie backward”
– at beginning
• all matter within small region (single point)
• very, very hot
• Subsequent expansion
–
–
–
–
called Big Bang
not an explosion
galaxies not moving (flying apart)
space is expanding
• Age of the Universe
To = 1/H (Hubble time)
~ 14 billion years
Big Bang Model
• Early universe very hot, very dense (mostly radiation)
• As it expanded, it cooled
• Eventually, atomic nuclei form
– when universe about 3 minutes old
– only simple atoms (hydrogen [deuterium], helium, lithium)
• Later, matter becomes transparent
– light escapes
– produces continuous spectrum (blackbody)
• cosmic microwave background radiation (CMB)
• Much later, stars and galaxies form
Evidence for the
Big Bang
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1.
2.
Expanding universe
Cosmic Background Radiation
–
–
–
3.
discovered by Penzias & Wilson in
1960’s (won Nobel Prize 1978)
light released when matter became
transparent
Observed background matches
predicted temperature (3 K)
Nucleosynthesis
–
–
–
Model predicts Universe is 75%
hydrogen, 25% helium.
Matches observed abundances
Details provide strong evidence
Fate of the Universe
• Big Bang: 3 possible fates
– depends on mass (=gravity) of Universe
– open universe (the Big Chill)
• not enough mass to stop the expansion
• universe expands forever
– flat universe
• exactly enough mass to stop the expansion, but in infinite time
– closed universe (the Big Crunch)
• enough mass to stop expansion
• followed by contraction back to single point
• Latest results (Supernova Cosmology)
– Indicate that the Universe is ACCELERATING!
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Current Status
• Careful tests via CMB
observations
– Universe is flat
– 4% normal matter
• 0.3% is luminous
– 23% dark, exotic matter
• what is it?
– 73% dark energy
• produces anti-gravity
• expansion rate is increasing
• what is it?
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