Date post: | 25-Dec-2015 |
Category: |
Documents |
Upload: | lindsey-pope |
View: | 217 times |
Download: | 1 times |
Outline
• A brief history of the Universe
• The Sun’s Early History– How do stars form?– Isotopes in the pre-solar
nebula– The birth of the Sun
• The middle-aged Sun– The star we know– Looking inside the Sun– The Sun in time
• As the Sun grows old– Red giant– Planetary nebula– White dwarf
• The distant future
BIG BANG – 13.7 billion years ago, space, time, and energy burst into existenceVery smallVery dense
Why?
INFLATION ERA – the universe explodes from smaller than an atom to the size of a grapefruit. Expansion slows when the driving force is transformed into matter and energy
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 - visible light, X rays, radio waves and ultraviolet rays. Energy transforms into matter:
•quarks•protons and neutrons •helium, deuterium and lithium
• The Universe was dominated by energy.• 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.
Origin of the Cosmic Microwave Background Radiation – the glow of the original, hot matter of the Universe
A uniform, faint microwave signal all over the sky
What are we seeing in the baby
picture?
The microwave radiation comes from the time when the temperature of the Universe became low enough for atoms to form Matter became transparent, allowing light to travel great distances It is like seeing the bottom layer of clouds on an overcast day.
STELLIFEROUS ERA – the current era
• Electrons combined with existing nuclei to form atoms, mostly hydrogen and helium
• Atoms condensed into the first generation of stars during the first 200 million years
• 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 Sun’s Early History
We know the Sun formed when the Universe was already more than 9 billion years old
How and why did the Sun form?
The Eta Carina Nebula has some of the Milky Way’s most massive stars
Stars are forming
continuously in the Galaxy
Star Formation!
Examining a Star Forming Region
Stars are born in cold, dense interstellar clouds
• cold gas• dust grains
The Great Nebulain Orion
Star formation is triggered when an interstellar cloud is compressed by a shock wave
• collision with another cloud• nearby supernova explosion• nearby hot star wind• disturbance from the Galaxy
Free Fall Contraction
As the cloud begins to collapse, it fragments into blobs that contract into individual stars.
The blobs glow faintly in radio or microwave light because they are very cool.
They gradually heat up as they contract and begin to glow in the infrared, but they remain hidden in the interstellar cloud.
Young stars are surrounded by dense disks of gas and dust
Disks have been imaged
with HST’s infrared camera
Basic facts:• 2-4 million years old• about 469 light-years distant• The disk is about 30 times the size of our solar systemWhy the window
pane appearance?
HST
Swirling disks around the
youngest starsThe collapsing protostar eventually heats up enough to slow the collapse through hydrostatic pressure, and blows away its cocoon.
What’s left is a T Tauri star, in the final stage of accretion of gas.
The Flying
Saucer
Star forming region 500 LY from Earth Dark, dusty disk seen edge-on About 300 AU across (or 5 times the diameter of Neptune's orbit) Central star is unseen
A young star in the Rho Ophiuchus dark cloud
Infrared false-color image from the ESO Antu telescope
Isotopes in the Pre-Solar Nebula
• Small mineral grains in meteorites contain evidence of long-decayed radioactive material
• The radioactive material decayed, and left rare forms of some elements in the rock
26Aluminum•13 protons•13 neutrons
26Magnesium•12 protons•14 neutrons
When we find an excess of 26Mg, we know 26Al must have been present
Half of the 26Al decays each 740,000 years
The Earliest Pre-Solar Grains
• Calcium-aluminum-rich inclusions
• Contains decay products of 26Al
• Ratio of original 26Al/27Al ratio allows us to date how long it took for the grain to form after the 26Al was created in a supernova explosion Formed 4,700,000,000 years ago
Grains Continued to Form
• Chondrules (grains found in primitive meteorites) also contain the “daughter products” of decayed 26Al
• Chondrules formed about 2 million years AFTER the CAl rich inclusions
Half life 740,000 years
Meteorites Once Contained 60Fe
• Troilite (FeS) grain in the Bishunpur meteorite
• Small nickel content allows detection of 60Ni, which decays from radioactive 60Fe
Half life 1.5 million years
Sun’s Formation Triggered by Supernova Explosion
• Radioactive material had to have been formed in the explosion of a massive star just before the Sun formed
• Material from the supernova explosion became incorporated into the pre-solar nebula
Extinct Isotopes in Early Solar Nebula Rocks
Radio-isotopeHalf Life(years)
DaughterIsotope
Reference Isotope
41Ca 100,000 41K 40Ca
26Al 740,000 26Mg 27Al
10Be 1,500,000 10B 9Be
60Fe 1,500,000 60Ni 56Fe
The Birth of the Sun
The Sun formed as part of a modest-sized cluster of stars
A nearby massive star exploded, creating radioactive elements
The explosion probably triggered the formation of the Sun
The Birth of the Sun
• The young cluster Messier 103
– in direction of the constellation Cassiopeia
– a distance of about 8000 light-years
– diameter of about 14 light-year
– age of over 20 million years old
The Visible “Surface” of the Sun
Sunspots• cooler regions• magnetic fields• prominences originate from active regions
The Sun’s Outer Atmosphere:
The Chromosphere and Corona
• Temperatures over a million degrees
• Magnetic fields• The solar wind
The Chromosphereis red because of emission from the hydrogen alpha line
dense jets of gas that shoot up from the
chromosphere
coronal
hole
The Corona is the outer layer of the Sun’s atmosphere, with a temperature of a million degrees or more
The corona is heated by the
twisting loops of magnetic field
massejectio
n
The Solar Magnetic Field
Helioseismology
With helioseismology, we can measure temperature, pressure and motion inside the Sun from sound waves that traverse the Sun’s interior.
Listen to the Sun
The Composition of the Sun
everythingelse
90% hydrogen atoms
10% helium atoms
Less than 1% everything else(and everythingelse is made in stars!)
The Sun in Time
n
The Sun in Time
Luminosity of the Sun
0
1
2
3
4
5
0 2 4 6 8 10 12Time since Formation (Billions of Years)
Bri
gh
tne
ss
The Sun is gradually growing brighter over time, as it converts helium into hydrogen
Eventually…
Stellar Evolution –
Studying the Lives of
Stars
• To learn about the future of the Sun, we must study other stars…
Stars according to Goldilocks
• The most massive stars form first • Some stars have 100 times the mass
of the Sun• Most stars are smaller than the Sun• Stars lower than 0.08 solar mass
(called brown dwarfs) cannot fuse hydrogen and simply cool off
Evolution of a Very Low Mass Star
•Very low mass stars (30% of the mass of the Sun), have “lifetimes” of 100’s of billions of years before they consume their hydrogen
๏
The Most Massive Stars
• The biggest stars in the Milky Way “live” only a few million years before using up their hydrogen
• Found in star clusters near the center of the Galaxy• 2-4 million years old
• masses more than 100 Suns
• they will explode as supernovae
• the remaining cluster stars will scatterBigger stars are “too bright” to form
Evolution of a Just-Right Star
• The Sun will burn its hydrogen for about 10 billion years before it runs out
• The hydrogen fusion reactions take place in the core
• When the hydrogen in the core is used up– the core SHRINKS– the star EXPANDS!
The Sun Becomes a Red Giant
When the helium core contracts, the surrounding hydrogen puffs up and the star becomes a red giant.
The Sun as a Red
Giant
The Sun today
The Sun as a red giant
Astronomers aren’t sure how big the Sun will grow when it becomes a red giant. It may become as large as the orbit of Venus, or even the Earth
The orbit of Venus
• Eventually, the outer layers blow off, exposing the hot central core of the star
• The hot central core heats the escaping gas and causes it to glow
• The central core becomes a “white dwarf” star, very dim and faint
The End of the Red Giant Phase
What’s Left? A White Dwarf
• About half the mass of the Sun
• the other half is blown away
• The size of the Earth
• Density of 1-2 tons per cubic centimeter
• Composed of carbon and oxygen
• little or no hydrogen or helium
Sirius B
Sirius in X-rays
The End of Sun-Like Stars
What about the Earth?
OrdinaryStar
RedGiant
PlanetaryNebula
White Dwarf
Fire and Ice!
If the Earth survives the red giant phase, then our world will be come cold and dark.
The Universe in a Day
Event 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 Less
Quantum 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 .
Websites of Interest Indiana Astronomical Society
www.iasindy.org National Optical Astronomy Observatory Image
Gallery www.noao.edu/image_gallery
Hubble Space Telescope Images www.hubblesite.org
Amazing Space amazing-space.stsci.edu
NASA’s Astronomy Picture of the Day antwrp.gsfc.nasa.gov
Astronomical Society of the Pacific www.astrosociety.org
The Stonebelt Stargazers www.mainbyte.com/stargazers/