Download - Stellar Evolution
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Stellar EvolutionFrom protostars to supernovas
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Protostars• Large nebulas of gas that begin to collapse or
contract heat up as atoms interact, causing them to glow.
• Once an opaque structure forms, it is considered a protostar.
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Protostar Structure• As a protostar collapses, an accretion disk forms
around the protostar, and jets of electromagnetic radiation erupt from the poles.
• Jet• Accretion Disk
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Brown Dwarf• When a protostar doesn’t have enough mass
to cause large scale hydrogen fusion, it forms a small Brown Dwarf star.
• Brown Dwarfs glow dimly, and are only a little bit larger than some planets.
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Red Dwarf• A Red Dwarf is less than half a solar mass.• It has convection currents in its core and envelope.• It is relatively cool and dim.• They are the most common stars that are visible.
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Sun-like stars
• Sun like stars are similar in mass to our Sun.• The sun is a yellow dwarf star.• It has several layers.
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Corona• Corona – The outermost layer, it is the second
hottest at 4000 K. It is made of gases moving away from the sun, also known as the solar wind.
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Chromosphere• The second layer of the sun.• The chromosphere is the thin lower layer of
the atmosphere.• Solar flares and prominencesoriginate in the
chromosphere.
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Photosphere• The gaseous surface of
the sun.• The photosphere absorbs
heat energy from lower layers, and then releases the energy as light (electromagnetic energy.)
• It is the part of the sun that visibly glows.
• Cooler areas in the photosphere are darker, and are called sunspots.
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Convection Layer
• The next layer absorbs light and heat from below.
• As it warms, convection currents are created that transfer heat from the inner layers to the photosphere.
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Radiative layer• The radiative layer is
extremely dense.• Electromagnetic x-rays are
absorbed from the core, re-emitted, and reabsorbed.
• It takes light millions of years to work its way through the radiative layer.
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The core• The core is under such intense pressure from the layers pressing from above due to gravity.
• The pressure is sufficient to cause nuclear fusion.
• This releases tremendous amounts of energy as gamma ray electromagnetic radiation.
• The outward force from fusion reactions keeps gravity from further collapsing the star.
• The inward pressure from gravity keeps the fusion reactions from exploding the star.
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Red Giants
• These are stars that are between 0.3 to 6 solar masses.
• Red giants form when all the hydrogen in a star’s core has fused to make helium. At this point, fusion stops, and gravity becomes the dominant force.
• As the core contracts due to gravity, it heats up, releasing more energy to the radiative layer.
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Red Giants 2
• As the radiative layer absorbs energy from the collapsing core, it also heats up until the pressure is enough to start hydrogen fusion in the outer layers.
• The outward pressure from energy released by fusion in the outer layers causes the star to expand, causing it to grow to as much as 200 times larger.
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White dwarf
• White dwarves form when a Red Giant fuses the last of its hydrogen in its outer layers.– The outer layers heat up and expand to form a
planetary nebula, which slowly drifts apart.– The inner core is left, slowly cooling and becoming
darker until it forms a Black Dwarf.
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Supernovas: Type 1a
• If a white dwarf star absorbs enough new matter, its mass can increase enough to allow gravity to cause the heavy elements in the core to begin fusion.
• Sometimes the resulting energy release is then enough to blow the star apart in a massive explosion.
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Blue Supergiants
• Blue supergiants are extremely hot and extremely dense.
• They have enough gravity to fuse heavier elements such as Helium and Lithium to make elements as heavy as Iron.
• They have very short lifespans before they fuse all the elements they can.