Transcript

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Dave Conley

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Star Basics The universe is full of stars.  Somewhere between approximately 1022 and 1024 stars are currently believed to exist. That’s more stars than grains of sand on the Earth! Stars are probably the most important objects in the universe.  Every element larger than helium comes from stars. We are technically stardust.

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Star Formation Clumps of mostly hydrogen form large molecular clouds inside nebulas. As they accrete more matter, the core becomes denser and becomes a protostar. Eventually, the mass reaches a critical point at which the internal temperature is hot enough to ignite nuclear fusion. The energy released from nuclear fusion stabilizes the star against it’s massive gravity.

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Star Size The sun and planets. The sun to VY Canis Majoris VY Canis Majoris is the largest known star. An estimated 9 billion suns could fit inside it!1

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Star Death Stars will last as long as they have fuel to burn. Most stars, like the Sun, are fueled from the nuclear fusion of hydrogen into helium in the star’s core.  This occurs at around 10-15 million K in the sun, and around 100 million K on earth.3 When fusion stops, there is no longer enough internal pressure to hold the star up against it’s own gravity and the star begins to collapse.

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Star Death II In about 5 billion years, the Sun will enter a red giant phase, initiating the end of it’s life cycle. This occurs when all of the hydrogen in the core is fused into helium. The lack of pressure in the core allows the star to compress, which begins heating the star further. This heat allows fusion in the outer shell of the core to begin, and the star swells tremendously. At it’s maximum size, the Sun’s perimeter will just engulf the Earth, disintegrating it.

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Supernovae Stars at least 8 times the mass of the Sun undergo a more epic finale called a supernova. There are many types of supernovae, but in any case they are the most energetic explosions in the known universe. During a supernova, a massive star can eject more energy than the Sun will put out in it’s entire lifetime. This is an equivalent of 200 trillion trillion 100 megaton H-bombs going off in a matter of seconds.4

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Core Collapse Supernovae Massive stars undergo core collapse, resulting in a type-II supernova. Process:  All of the stars hydrogen fuses into helium; fusion ceases, diminishing internal pressure.  Gravity overpowers the internal pressure and crushes the core, heating it up further.  Eventually, heat and pressure are strong enough to fuse helium into carbon, and the process repeats, fusing atoms into new heavier elements.  This continues up to iron. The atomic structure of iron causes it to absorb energy during fusion.  Gravity overcomes the star, and a major collapse occurs

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Core Collapse Supernovae II The inner core collapses in ¼ of a sec from the size of the Sun to the size of Manhattan. The outer layers falling in nearly as fast, collide with this new core and rebound with a force comparable to nothing else in the universe. The speed and intensity of the ejected outer layers can outshine the entire surrounding galaxy for several weeks. The blast is so powerful, it creates all of the elements heavier than iron, spewing them deep into space.

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Neutron Stars The remnant cores of these supernovae collapse into neutron stars. At this stage, the force of gravity is so strong, it overcomes the repulsion of electrons. In the core of the star, electrons are combined with protons to make neutrons and expel neutrinos. The star becomes stable from the internal pressure of the neutron repulsion. The result is the remnants of a star so dense, a teaspoon of it would weight around 10 billion tons on earth!

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Other Types of Neutron Stars Pulsars-  Neutron stars spin so fast (100’s of times a second) that electrons caught in the intense magnetic field heat up and emit radiation out of the poles.  All neutron stars do this, but the radiation can only be seen if the beam faces the earth, making it appear to pulsate.

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Magnetars The most magnetic objects in the universe. Magnetars are believed to form when a neutron star is created with a very fast spin. The phenomenon known as dynamo action causes an intense magnetic field around the star from the convection of ionized gas. ‘Starquakes’ in the crust of the star disrupt this field and the star emits massive amounts of magnetic energy. If within a 1000 miles, a magnetar would rip the iron from your blood!

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Black Holes The ultimate in star death. Stars at least 20 times the mass of the Sun end their lives as black holes. Currently, physicists can only speculate what happens at the center of black holes.

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Black Holes II When the cores of the largest stars collapse, they have such enormous gravity that the repulsion of even neutrons can’t withstand it. At this point, the force of gravity is so strong that not even light can escape it. Theoretically, with an infinite density, it can even warp time itself. There is much about black holes that can’t be explained with our current understanding of physics. The current laws of physics cannot explain what happens at the center of black holes, though there are many interesting theories.