A105 Stars and Galaxies

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Today’s APOD

Principles of CosmologyHomogeneity – 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

UniverseCourtesy of Fred AdamsUniversity of Michigan

BIG BANG – 13.7 billion years ago, space, time, and energy burst into existenceThe 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.

• Originally, no stars• Protons and electrons combined into atoms• The Universe became opaque due to absorption of

light by hydrogen atoms

The First Dark Era

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 DayEvent When it happenedBig 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 ERAThe 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 LessQuantum fluctuation. Inflation. Expansion. Strong nuclear interaction. Particle-antiparticle 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

• 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

When did life arise on Earth?

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

•For liquid water to exist, a planet needs to be the right distance from the star. WHY?

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.

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

Gas Giants

Ice Giants

Terrestrial Planets

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...

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