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The Past and Future History of the Sun Mini-University 2004 • 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 Outline • As the Sun grows old – Red giant – Planetary nebula – White dwarf • The distant future A Brief History of the Universe BIG BANG – 13.7 billion years ago, space, time, and energy burst into existence Very small Very 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? Star Formation! Stars are forming continuously in the Galaxy The Eta Carina Nebula has some of the Milky Way’s most massive stars Examining a Star Forming Region The Great Nebula in Orion Stars are born in cold, dense interstellar clouds • cold gas • dust grains 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. The Cone Nebula Examining a Star Forming Region Disks have been imaged with HST’s infrared camera Young stars are surrounded by dense disks of gas and dust Swirling disks around the youngest stars HST Basic facts: • 2-4 million years old • about 469 light-years distant • The disk is about 30 times the size of our solar system Why the window pane appearance? The 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 A young star in the Rho Ophiuchus dark cloud Infrared false-color image from the ESO Antu telescope 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 Dust grains form around the young star Isotopes in the Pre-Solar Nebula • Small mineral grains in meteorites contain evidence of longdecayed 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 Formed 4,700,000,000 years ago explosion 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-isotope Half Life (years) Daughter Isotope 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 lightyear – age of over 20 million years old The Middle-Aged Sun: The Star We Know The Visible “Surface” of the Sun Sunspots • cooler regions • magnetic fields • prominences originate from active regions • Temperatures over a million degrees The Sun’s Outer Atmosphere: The Chromosphere and Corona • Magnetic fields • The solar wind The Chromosphere is red because of emission from the hydrogen alpha line dense jets of gas that shoot up from the chromospher e The Corona is the outer layer of the Sun’s atmosphere, with a temperature of a million degrees or more coronal hole mass ejectio n The corona is heated by the twisting loops of magnetic field The Solar Magnetic Field Looking inside the Sun Listen to the Sun: Listen to the Sun 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 Inside the Sun: Energy and Motion The energy comes from nuclear fusion reactions in the Sun’s core The Composition of the Sun 90% hydrogen atoms 10% helium atoms Less than 1% everything else (and everything else is made in stars!) everything else The Sun’s Energy Comes from Nuclear Fusion Watching the Far Side of the Sun The Sun in Time n 5 The Sun in Time Brightness 4 3 The Sun is gradually growing brighter over time, as it converts helium into hydrogen Luminosity of the Sun 2 1 0 0 2 4 6 8 10 Time since Formation (Billions of Years) 12 Eventually… As the Sun Grows Old… 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 Bigger stars are “too bright” to form • the remaining cluster stars will scatter 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 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 Sun today The Sun as a red giant The orbit of Venus The End of the Red Giant Phase • 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 Planetary Nebulae! 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 Ordinary Star The End of SunLike Stars Red Giant Planetary Nebula What about the Earth? Fire and Ice! White Dwarf If the Earth survives the red giant phase, then our world will be come cold and dark. The Evolution of Stars 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 . 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/