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Susan Cartwright Our Evolving Universe 1
The story so farThe story so far
We have consideredWe have considered the origin of the Universethe origin of the Universe the formation and evolution the formation and evolution
of galaxiesof galaxies the birth, life and death of the birth, life and death of
starsstars How does this relate to the How does this relate to the
existence of the solar existence of the solar system and of life on Earth?system and of life on Earth?
Susan Cartwright Our Evolving Universe 2
Observation and theoryObservation and theory
Astronomy is an Astronomy is an observational scienceobservational science
theories need support theories need support from observationsfrom observations
cosmologycosmology expansion of universe from expansion of universe from
Doppler shiftDoppler shift primordial abundances primordial abundances
from old stars, ancient from old stars, ancient hydrogen clouds, etc.hydrogen clouds, etc.
properties of microwave properties of microwave backgroundbackground
large-scale structurelarge-scale structure microwave backgroundmicrowave background galaxy surveysgalaxy surveys
galaxiesgalaxies observation of distant observation of distant
galaxiesgalaxies detailed study of nearby detailed study of nearby
galaxies and Milky Waygalaxies and Milky Way starsstars
detailed study of Sundetailed study of Sun studies of stellar clustersstudies of stellar clusters spectroscopic observationsspectroscopic observations
evidence for nucleo-evidence for nucleo-synthesis, age, etc.synthesis, age, etc.
Probably some of the Probably some of the material in this course is material in this course is wrongwrong
we just don’t know whatwe just don’t know what
Susan Cartwright Our Evolving Universe 3
In the beginning….In the beginning….
Our universe began about 15 billion years Our universe began about 15 billion years agoago brief period of exponential expansion ~10brief period of exponential expansion ~10-35-35 s s
after initial big bang resulted in nearly flat, after initial big bang resulted in nearly flat, very uniform visible universe todayvery uniform visible universe today
inflationinflation after this after this
universeuniverseexpands expands much moremuch moreslowlyslowly
WMAPWMAP
Susan Cartwright Our Evolving Universe 4
In the beginning….In the beginning….
Continuing expansion Continuing expansion causes universe to coolcauses universe to cool in a few minutes cools in a few minutes cools
enough to form the light enough to form the light isotopes isotopes 22H, H, 33He, He, 44He, He, 77LiLi
observations of these isotopes observations of these isotopes test theorytest theory
after 300000 years cools after 300000 years cools enough for neutral atoms to enough for neutral atoms to formform
microwave background microwave background radiation emittedradiation emitted
its properties probe conditions its properties probe conditions in early universein early universe
Ken Nollett, CaltechKen Nollett, Caltech
Susan Cartwright Our Evolving Universe 5
The formation of structureThe formation of structure
Tiny irregularities in the early Tiny irregularities in the early Universe are seen in the Universe are seen in the micro-wave backgroundmicro-wave background
denser patches would have denser patches would have had slightly stronger gravity, had slightly stronger gravity, attracting material towards attracting material towards themthem
seeds of structure formationseeds of structure formation produce small protogalaxies produce small protogalaxies
which interact and merge to which interact and merge to form modern galaxiesform modern galaxies
Simulation by the Los Alamos Simulation by the Los Alamos theoretical astrophysics grouptheoretical astrophysics group
Susan Cartwright Our Evolving Universe 6
The galaxiesThe galaxies
The Milky Way is a large The Milky Way is a large spiral galaxyspiral galaxy
it has a bulge, disc and it has a bulge, disc and halohalo
most of its mass is most of its mass is apparently dark matterapparently dark matter
it is located in a small it is located in a small group on the fringes of the group on the fringes of the large Virgo clusterlarge Virgo cluster
Other galaxies have had Other galaxies have had more turbulent historiesmore turbulent histories
collisions and mergers collisions and mergers play important roles in play important roles in galaxy evolutiongalaxy evolution
Susan Cartwright Our Evolving Universe 7
The starsThe stars
Stars form when cool, dense Stars form when cool, dense clouds of interstellar gas clouds of interstellar gas collapse under gravitycollapse under gravity
they spend most of their they spend most of their lives on the main sequence lives on the main sequence fusing hydrogen to heliumfusing hydrogen to helium
eventually they expel their eventually they expel their outer regions as planetary outer regions as planetary nebulae or supernovaenebulae or supernovae
thus disseminating heavy thus disseminating heavy elements into the elements into the interstellar gasinterstellar gas
Susan Cartwright Our Evolving Universe 8
The elementsThe elements
The top ten elements:The top ten elements:H 100.000 big bang big bang
He 9.700 big bang big bang
O 0.085 He fusion supernovae
C 0.036 He fusion planetarynebulae
Ne 0.012 C fusion supernovae
N 0.011 H fusion planetarynebulae
Mg 0.004 Ne, Cfusion
supernovae
Si 0.004 O fusion supernovae
Fe 0.003 supernovae supernovae
S 0.001 O fusion supernovae
Note that the most common Note that the most common elements in your body all occur elements in your body all occur in the top ten, formed by a in the top ten, formed by a variety of mechanisms (most variety of mechanisms (most obvious absentees are calcium obvious absentees are calcium and phosphorus)and phosphorus)
production
dissemination
Susan Cartwright Our Evolving Universe 9
A hospitable universe?A hospitable universe?
The universe is >10 The universe is >10 billion years oldbillion years old
did not expand so fast did not expand so fast stars never formedstars never formed
did not recollapse in did not recollapse in rapid Big Crunchrapid Big Crunch
There is an asymmetry in There is an asymmetry in the interactions of matter the interactions of matter and antimatterand antimatter
they do not entirely they do not entirely cancel each other outcancel each other out
universe has significant universe has significant matter contentmatter content
We have “friendly” We have “friendly” nuclear physicsnuclear physics
22H is stable, but H is stable, but 22He isn’tHe isn’t stars work!stars work!
1212C has an energy level C has an energy level at just the right placeat just the right place
carbon is a common carbon is a common elementelement
supernovae explodesupernovae explode heavy elements are heavy elements are
incorporated into new stars incorporated into new stars and planetsand planets
Susan Cartwright Our Evolving Universe 10
Observations and observersObservations and observers
No obvious reasons for No obvious reasons for “lucky” values of many “lucky” values of many parametersparameters
new physics?new physics? reasons are there, but we reasons are there, but we
don’t yet know themdon’t yet know them selection biasselection bias
if values were not “lucky”, if values were not “lucky”, universe would not permit universe would not permit intelligent life to evolveintelligent life to evolve
we existwe exist therefore, parameters must therefore, parameters must
have “lucky” valueshave “lucky” values
...weak anthropic principle...weak anthropic principle
Why look for physics Why look for physics reasons?reasons?
anthropic principle anthropic principle arguments less fruitfularguments less fruitful
useful scientific theories useful scientific theories explain existing data explain existing data andand make testable predictionsmake testable predictions
leads to deeper leads to deeper understanding of natureunderstanding of nature
more elegant/satisfyingmore elegant/satisfying
Susan Cartwright Our Evolving Universe 11
A planet-building universeA planet-building universe
Massive stars produce Massive stars produce heavy elementsheavy elements
and disseminate them and disseminate them into interstellar medium into interstellar medium via planetary nebulae via planetary nebulae and supernovaeand supernovae
Heavy elements in cool Heavy elements in cool gas tend to clump gas tend to clump together to form small together to form small dust grainsdust grains
reason for opacity of gas reason for opacity of gas clouds in Milky Wayclouds in Milky Way
Theory and observation Theory and observation (cratering record) (cratering record) suggest planets of solar suggest planets of solar system formed by system formed by accretionaccretion
dust grains collide and dust grains collide and stick to form stick to form successively larger successively larger bodiesbodies
probably fairly easy probably fairly easy process if stars form process if stars form from dust-rich materialfrom dust-rich material
Susan Cartwright Our Evolving Universe 12
Planetary systemsPlanetary systems
Many young stars are surrounded by dusty discsMany young stars are surrounded by dusty discs theory suggests these should develop into planetary theory suggests these should develop into planetary
systemssystems Over 200 planets have now been observed around other Over 200 planets have now been observed around other
starsstars planetary systems are relatively common planetary systems are relatively common
at least around stars with high heavy element contentat least around stars with high heavy element content little evidence about howlittle evidence about how
typical our system istypical our system is current detection methodscurrent detection methods
biased against systemsbiased against systemslike ourslike ours
… … next lecture!next lecture!Mike Ressler, NASA/JPL