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A105
Stars and Galaxies
Today’s APOD
 Last units: 81, 82, 83, 84
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Principles of Cosmology
Homogeneity – Matter
is spread uniformly
through space
Isotropy – The Universe
looks the same in every
direction
Universality – The basic principles of
physics are the same everywhere
The Cosmological Principle: The universe
will look more or less the same to
observers everywhere, in every galaxy, no
matter where it is
Applying the Principles of Cosmology
Summary – Strong evidence
supports the Big Bang Theory
• The Universe is expanding (and cooling) from an
initial, dense state
• Radiation left over from the Big Bang is now
detected in the form of microwaves—the cosmic
microwave background—which we can observe
with a radio telescope
• Observations of helium and other light elements
agree with the predictions for fusion in the Big
Bang theory
A brief history
of the
Universe
Courtesy of Fred Adams
University of Michigan
BIG BANG – 13.7 billion years ago, space,
time, and energy burst into existence
The part of the Universe that
now comprises our “observable
universe” was very small and very
dense
Why did the Universe suddenly appear????
INFLATION ERA – Regions of the universe rapidly expand
from smaller than an atom to bigger than the Solar System.
Because all of space was so compact, every part
of the universe was in “contact” with every
other part.
Energy was uniformly distributed throughout
the early universe
PHOTON ERA - energy in the form of electromagnetic
radiation dominates the Universe - visible light, X rays,
radio waves and ultraviolet rays. Energy transforms into
matter:
• quarks
• the first nuclei: protons, neutrons,helium
•The density of energy was so great that matter could
not exist.
• As the density was gradually reduced through
expansion, matter began to form.
• Both matter and anti-matter formed, but for some
reason, there was a slight excess of matter.
The First Dark Era
• Originally, no stars
• Protons and electrons combined into atoms
• The Universe became opaque due to absorption of
light by hydrogen atoms
Origin of the CMB – the thermal
radiation of the first atoms
Isotropic microwave
radiation
STELLIFEROUS ERA – the current era
• Atoms condensed into the first generation of
stars during the first 200 million years
•The first stars reheated the gas (reionization)
• The universe remains transparent because the
density is so low
•
•
•
•
Galaxies formed
Sun, solar system formed 4.6 billion years ago
Life appeared on Earth 3.8 billion years ago
Modern humans show up just 100,000 years ago
The Universe in a Day
Event
When it happened
Big Bang
12:00:00 midnight
First Atoms form
12:00:08 a.m.
Stars and Galaxies form
12:29 a.m.
Our Sun, Earth, Moon are born
4:00 – 4:48 p.m.
Earliest life on Earth
6:00 p.m.
First multi-cellular life on Earth
10:53 p.m.
Dinosaurs appear
11:40 p.m.
Dinosaurs die
11:54 p.m.
Humans arise
11:59:56 p.m.
Present Day
12:00 midnight tomorrow
Sun becomes Red Giant
8:00:00 a.m. tomorrow
Sun becomes White Dwarf
8:19:00 a.m. tomorrow
DEGENERATE ERA –
10 trillion trillion trillion years after the Big Bang
• Planets detach from stars
• Stars and planets evaporate from
galaxies
• Most ordinary matter in the universe is
locked up in degenerate stellar remnants
• Eventually, even the protons themselves
decay
BLACK-HOLE ERA 10,000 trillion trillion trillion trillion trillion
trillion trillion trillion years after the Big
Bang
• The only large objects remaining are
black holes
• Eventually even the black holes
evaporate into photons and other types of
radiation.
The Final DARK ERA –
Only photons, neutrinos, electrons and positrons
remain, wandering through a universe bigger than
the mind can conceive.
Occasionally, electrons and positrons meet and
form "atoms" larger than the visible universe is
today.
From here into the infinite future, the universe
remains cold, dark and empty.
The History of the Universe in 200 Words or Less
Quantum fluctuation. Inflation. Expansion. Strong nuclear interaction. Particleantiparticle annihilation. Deuterium and helium production. Density perturbations.
Recombination. Blackbody radiation. Local contraction. Cluster formation.
Reionization? Violent relaxation. Virialization. Biased galaxy formation? Turbulent
fragmentation. Contraction. Ionization. Compression. Opaque hydrogen. Massive star
formation. Deuterium ignition. Hydrogen fusion. Hydrogen depletion. Core
contraction. Envelope expansion. Helium fusion. Carbon, oxygen, and silicon fusion.
Iron production. Implosion. Supernova explosion. Metals injection. Star formation.
Supernova explosions. Star formation. Condensation. Planetesimal accretion.
Planetary differentiation. Crust solidification. Volatile gas expulsion. Water
condensation. Water dissociation. Ozone production. Ultraviolet absorption.
Photosynthetic unicellular organisms. Oxidation. Mutation. Natural selection and
evolution. Respiration. Cell differentiation. Sexual reproduction. Fossilization. Land
exploration. Dinosaur extinction. Mammal expansion. Glaciation. Homo sapiens
manifestation. Animal domestication. Food surplus production. Civilization! Innovation.
Exploration. Religion. Warring nations. Empire creation and destruction. Exploration.
Colonization. Taxation without representation. Revolution. Constitution. Election.
Expansion. Industrialization. Rebellion. Emancipation Proclamation. Invention. Mass
production. Urbanization. Immigration. World conflagration. League of Nations.
Suffrage extension. Depression. World conflagration. Fission explosions. United
Nations. Space exploration. Assassinations. Lunar excursions. Resignation.
Computerization. World Trade Organization. Terrorism. Internet expansion.
Reunification. Dissolution. World-Wide Web creation. Composition. Extrapolation?
Copyright 1996-1997 by Eric Schulman .
Astronomy and
Life in the Universe
When did life arise on Earth?
How did life arise on Earth?
What are the necessities of life?
Scientific Study of Life
Goals:
To present what observations of the
physical world tell us about the origin
and development of life
To use that information to suggest what
we might expect to find elsewhere in the
Universe and how to search for life
elsewhere
When did life arise on Earth?
• Life probably arose on Earth more than 3.85 billion
years ago, shortly after the end of heavy
bombardment
• Evidence comes from fossils and carbon isotopes
Earliest
Fossils
• Oldest fossils show that bacteria-like organisms
were present over 3.5 billion years ago
• Carbon isotope evidence pushes origin of life to
more than 3.85 billion years ago
The Origin of
Life on Earth
• Life on Earth is about 3.5
billion years old
• Life arose nearly as soon as
conditions allowed
– surface conditions were too
hostile before this point
• Early life was very simple
– single cell algae
• Multicelled life arrived about
1 billion years ago
– simple sponges
• Complexity increased
• More advanced forms seem
to survive more easily
Tree of Life
• Mapping genetic
relationships has led
biologists to discover
this new “tree of life.”
• Plants and animals are
a small part of the tree.
• Suggests likely
characteristics of
common ancestor.
• These genetic studies suggest that the earliest
life on Earth may have resembled the bacteria
today found near deep ocean volcanic vents
(black smokers) and geothermal hot springs .
Laboratory Experiments
• Miller-Urey
experiment (and
more recent
experiments)
show that
building blocks of
life form easily
and
spontaneously
under conditions
of early Earth.
Origin of Oxygen
• Cyanobacteria
paved the way for
more complicated
life forms by
releasing oxygen
into atmosphere
via photosynthesis
Brief History of Life
• 4.4 billion years - early oceans form
• 3.5 billion years - cyanobacteria start releasing
oxygen.
• 2.0 billion years - oxygen begins building up in
atmosphere
• 540-500 million years - Cambrian Explosion
• 225-65 million years - dinosaurs and small
mammals (dinosaurs ruled)
• Few million years - earliest hominids
Necessities for Life
• Nutrient source
• Energy (sunlight, chemical reactions,
internal heat)
• Liquid water (or possibly some other
liquid)
Hardest to find
The
Habitable
Zone
Too hot!
Too cold!
A habitable world
contains the basic
necessities for life as
we know it, including
liquid water.
It does not necessarily
have life.
•For liquid water to exist, a planet
needs to be the right distance from the
star. WHY?
What
else do
we
need?
•The orbits of the planets must be stable, and not too
eccentric
•The planet needs to have the right mass--too small and
the atmosphere escapes--too large and the atmosphere
is made of hydrogen
•The atmosphere needs to be of the right mix of
greenhouse gases
Anything else?
•A Jupiter-like neighbor is nice to
catch most of the asteroids and
comets that would otherwise hit the
planet
•The planet needs the right tilt-currents mix nutrients--a Uranus tilt
would not work
•A large Moon stabilizes the planet and
creates water tides for sloshing
around nutrients
Our Solar System
Terrestrial
Planets
Ice Giants
Gas Giants
Searches for Life on Mars
• Mars had liquid water in the distant past
• Still has subsurface ice; possibly subsurface
water near sources of volcanic heat.
In 2004, NASA Spirit
and Opportunity
Rovers sent home new
mineral evidence of
past liquid water on
Mars.
The Martian Meteorite debate
composition indicates
origin on Mars
•
•
•
•
1984: meteorite ALH84001 found in Antarctica
13,000 years ago: fell to Earth in Antarctica
16 million years ago: blasted from surface of Mars
4.5 billion years ago: rock formed on Mars
• Does the meteorite contain fossil
evidence of life on Mars?
… most scientists not yet convinced
Could there be life on Europa
or other jovian moons?
• Ganymede, Callisto also show some
evidence for subsurface oceans.
• Relatively little energy available for life, but
still…
• Intriguing prospect of THREE potential homes
for life around Jupiter alone…
Ganymede
Callisto
Titan
• Surface too cold for liquid water (but deep
underground?)
• Liquid ethane/methane on surface
Saturn’s Moon Enceladus
• Cassini
spacecraft found
water geysers
Could life have
migrated to
Earth from
elsewhere in
the Solar
System?
• Venus, Earth, Mars have exchanged tons
of rock (blasted into orbit by impacts)
• Some microbes can survive years in
space...
 Last units: 81, 82, 83, 84