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Stars The Suns of Other Worlds What are Stars? • Giant • Luminous • Plasma. – Energized Gas • Powered by fusion of hydrogen or heavier elements • Stars are NOT burning – No oxygen How do we learn about Stars? • Studying the electromagnetic spectrum. • We can only see a tiny bit of the light stars produce. • Visible light • Stars emit lots of different kinds of ‘light’ How did we learn about the EMS? • Sir Isaac Newton • If you pass sunlight through a prism it separated out into a spectrum of all the colors Infrared Light • William Herschel discovered IR by accident. • Do colors have temperatures? • He found that an area just beyond the red part of the spectrum was hotter. • He named that invisible light infra-red meaning beyond red Ultraviolet (UV) Light • Johann Ritter • Found chemicals that darkened when exposed to sunlight had a greater reaction just above the violet end of the spectrum • Ultra-violet, meaning above violet. What can we learn about Stars? • • • • Mass Temperature Stage of Development Chemical Composition Star Light, Star Bright… • Absolute magnitude – How much light a star produces • Apparent magnitude – How much light actually makes to Earth • Absolute magnitude requires we know the distance to the star. How Far? • Parallax – The apparent movement of an object seen at different viewpoints. – The more the object moves (the greater the parallax), the closer it is. – The Hipparcos satellite Color • Color • Different Temperature – Mass – Temperature • Missing Color – Shows presence of other chemicals • Spectra – A view of the color produced by a star Hertzsprung-Russell Diagram • If you make a graph of stars brightness and color stars fall into certain areas • Stars move through these areas as they age Types of Stars • Two different methods – Temperature • Color alone – Age • Color and brightness • HR Diagram Temperature – – – – – – – O - 33,000K+ B - 10,500 - 30,000K A - 7,500 - 10,000K F - 6,000 - 7,200K G - 5,500 - 6,000K K - 4,000 - 5,250 M - 2,600 - 3,850K -bluest -bluish -blue-white -white -yellow white -orange -red HR Diagram • Four major groups – – – – Super Giants Giants Main Sequence White Dwarfs • Some ‘stars’ didn’t get graphed – – – – Neutron Stars Black Holes Black Dwarfs Brown Dwarfs Main Sequence Stars • • • • Dwarf stars Beginning of stars life Bigger, hotter stars spend less time here Fusing hydrogen as their main fuel. Giants • Larger(10x) and brighter than main sequence stars • Average main sequence stars that have run out of hydrogen for fusion. • Helium fusion is more explosive – outward pressure >inward Super Giants • Largest and brightest of all stars – 10-70 times size of the sun – 30,000+ times as bright as the sun • Large MSS that ran out of hydrogen • Short life spans White Dwarfs • The smallest and faintest of all stars – Stopped fusion process – Glow only due to stored energy • Mass of sun, size of earth • The final stage of most stars lives • Eventually cool to form Black Dwarfs Star Life Cycles • Nebula – birth place of stars • Protostars – baby stars – Gravity and fusion pressure not balanced yet – Brown Dwarf – failed star • MSS – first stage of a stars life • What happens next depends on mass of star Sun-like Stars • • • • Run out of hydrogen Outer layers expand Red giant Outer layers eventually drift off into space – Planetary nebula • Hot core remains as a White Dwarf • Hypothetically if heat is gone becomes a Black Dwarf Big Stars • Stars 1.5-3 times mass of sun • Become Red Super Giants • Fuse heavier elements until core is iron – Collapses, causes explosion • Super Nova – Create all other elements – Planets, people Neutron Stars • Neutrons. • 2x times mass of sun. • 20-40km – Extremely dense – Teaspoon - 5,000,000,000,000kg • Gravity makes surface perfectly smooth Giant Stars • • • • Also become red super giants. Same onion structure Same Super Nova If remaining core is >3 times the mass of the sun it forms a Black Hole • All the matter is squeezed into a space smaller than an atom. • Light can’t escape Black Hole • Any matter falling into a black hole produces deadly gamma rays. • Event Horizon – Distance from the center of the black hole beyond which nothing can escape • Spaghettification – Youtube video Star Structure • Stars are made of several layers that each have differing properties. – – – – – – Core Radiation Zone Convection Zone Photosphere Chromosphere Corona Core • Site of Nuclear Fusion • Extreme amounts of pressure • 10,000,000 K Radiation Zone • Pressure from the core balance pressure from above layers, particles don’t move. • Energy bounces around inside this layer for an average of 170,000 years. • 7-2,000,000 K Convection Zone • Energy moves with motion of plasma. • In main sequence stars, CZ is near the surface. • In giant stars it is right next to the core. • ~1,000,000 K Photosphere • Coolest Layer (6,000K) • Sun spots – Disruptions in magnetic field • Solar Flares – Violent explosions that send sub atomic particles into space. – Affect satellites, astronauts, power grids. Chromosphere • Atmosphere of sun • Hotter than photosphere due to magnetic activity. – 6-20,000 K Corona • 1,000,000 K • Extends out several million km. • Visible during solar eclipse