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