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---------------------- 2299 - You are made of stardust?.
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- As gravity draws stellar hydrogen together to form stars, the power of gravity forces the atoms together with enough strength to bond the nuclei together through nuclear fusion. Hydrogen is the simplest element with only a single proton nucleus and a single electron in orbit.
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- When all the hydrogen is fused together, it begins moving on to the higher elements, until eventually the star becomes nothing but a giant ball of iron.
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- All the hydrogen burns into helium in 10 million years.... All the helium burns to carbon in 1 million years.... Again, the star starts to collapse, because there's no more fuel. But then it heats up and the carbon starts to burn ... to form neon and nitrogen. And all of the carbon in the star burns in 100 thousand years.... And you get to oxygen. Oxygen ... burns to silicon in 10 thousand years.
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- It's getting hotter and hotter and hotter. Less efficient. And then when all the oxygen burns to silicon, you're in the last day of the star because, remarkably, it is so hot at that point that all of the silicon in the center of the star, many thousands of times the mass of the Earth, burns to form iron in one day....
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- Iron can't burn to form anything. Iron is the most tightly-bound nucleus in nature. So once that has happened, there's no more fuel... When all the silicon has burned to iron, suddenly the star realizes there's fuel left to burn and that interior of the star, which has been held up by the pressure of nuclear burning, collapses.
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- That whole collapse happens in one second.... There's a shock wave and that shock wave ... spews out all of the atoms that were created during the life history of a star. The carbon, the nitrogen, the helium, the iron.
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- And that's vitally important, because every atom in your body was once inside a star that exploded.... The atoms in your left hand probably came from a different star than in your right hand, because over 200,000,000 stars have exploded to make up the atoms in your body.
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- How do we know this? Because we've seen these supernovas happen. How frequently do these things happen? Stars explode once per hundred years per galaxy. Sounds like it's kind of hard to find these things, doesn't it? Consider this:
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- If you took a dime, held it at arms length up into a dark portion of the night sky, you'd be pointing your dime toward about 100 million galaxies. Many of these galaxies can be seen by our best telescopes.
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- This means that we would expect, in a given year, to see about a million galaxies that are having a supernova in it. If you take this reasoning further, there should be about 2,739 supernovas per day, or 114 supernovas per hour, or almost 2 supernovas per minute ... just in the region that you're able to cover up by holding up a dime.
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- Now, we aren't going to see all of those supernovas, but this gives an idea of how common these things are.
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- A Supernova is a sun, a star, that explodes because it becomes unstable after it exhaust all of its nuclear fuel. Our Sun will not become a Supernovae because it is not big enough.
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- A bigger star will have the gravity necessary to overcome the electromagnetic force between the electron and nucleus of atoms and when its fuel is gone it goes supernova. The explosions can be 1,000,000,000 times as bright as our Sun.
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- Supernova start out as a giant gas nebula that gradually takes shape, due to gravity, as a roughly spherical clump of gas and dust. Our Sun started out the same way but its gas cloud was only about one lightyear in diameter.
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- Supernova start out 10 to 100 times bigger. The cloud spins faster as it condenses, like an ice skater pulling in her arms as she spins, and flattens out in the shape of a disk.
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- A clump of a giant molecular cloud forms, rotating once every million years, has a radius of 0.05 lightyears. Over billions of years it condenses to the size of our solar system, 40 astronomical units (An AU equals the Sun-Earth distance).
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- Angular momentum is preserved so we can calculate the rotation rate.
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----------------------------- Angular Momentum = mass * angular velocity * radius^2
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----------------------------- The mass is constant so it drops out of the equation.
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---------------------------- Angular velocity = 2*pi*radius / period = one cycle / period
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------------------ One Cycle / 10^6 years * (0.5 LY)^2 = one Cycle / Period * (40AU)^2
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---------------------------- There are 63,240 AU in a light year
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-------------- One Cycle / 10^6 years * (3162 AU)^2 = one Cycle / Period * (40AU)^2
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----------------------------- 6249 * 10^-6 = 1 / Period
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----------------------------- Period = 160 years
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----------------------------- 160 years is about the period of Neptune which is 165 years.
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- The densest pocket of matter collects in the center of the swirling disk. A core condenses with swirling protons gaining more and more energy. The protons are the nucleus of hydrogen atoms that have lost their electrons and have a positive charge. With all like positive charges repelling each other the electromagnetic force keeps them apart.
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- Eventually, gravity wins and the protons are pulled closer together causing collisions that overcome the electromagnetic force and allow them to stick together. The protons are then stuck together with a strong nuclear bond.
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- When four protons weld together like this they form helium. This nuclear reaction is called helium fusion and when it happens 1% of the mass is left over and converts directly into energy. According to Einstein’s E=mc^2 equation, mass converts to energy by multiplying each kilogram times 90,000,000,000,000,000.
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- In the case of our Sun, 600,000,000 tons of hydrogen are converted to helium every second. Radiation is produced when atoms release stored energy. This energy is in the form of gamma rays.
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- Unlike sound waves electromagnetic waves, such as gamma rays, need no substance through which to travel. The wave’s alternating electric and magnetic fields travel through the vacuum of space at 300,000 kilometers per second.
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- The faster the waves alternate the higher the energy they carry. Gamma rays are the highest and we have yet to discover their frequency limit. The Sun’s energy begins as gamma rays in the core. As they reach the surface each ray spreads out as thousands of visible light photons, bathing the Solar System in heat and light.
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- At our Sun’s surface the gases are 1/10,000 the density of air. Halfway toward the center ( 250,000,000 miles deep ) the density is comparable to that of water. At the core, the density is 12 times that of lead and the temperature is 10,000,000 degrees.
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- The Supernova is much bigger than our Sun, the core is much denser, the temperatures much hotter, and the hydrogen burns much faster. The radiating intensity is 50,000 times brighter than our Sun. While our Sun will take 10 billion years to burn all its hydrogen, the Supernova will burn all its hydrogen in only 10 million years, 1000 times faster.
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- When this happens the star will expand to monstrous proportions. The hydrogen will be gone from the core and from the core out it will develop layers like onion skins. Helium will be burning at the core. When the helium is gone the next layer begins to fuse into carbon, then oxygen.
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- These heavier elements are squeezed inward and temperatures of 1 billion degrees begins to fuse carbon and oxygen into neon and magnesium. Each chemical group burns in concentric shells, forming silicon, sulfur, argon, calcium. The fusion proceeds up the periodic table until iron is formed. Fusions stops with iron.
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- Fusion stops because when iron ignites it cools the gas around it. Sounds strange to say cool when the collapsing core is still at 10 billion degrees. Instead of generating more power two iron nuclei require more energy to fuse. So, fusions stops.
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- To get energy out of elements heavier than iron you need “fission“, the splitting of atoms rather than fusing them together.
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- The iron at the core begins to disintegrate and temperatures reach 10 billion degrees. Without fusion to generate heat the iron can no longer withstand the force of gravity. In less than one second the core collapses from the size of the planet Mars to the size of a city, Manhattan. In the blink of an eye a “Neutron star” is formed.
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- A smaller star, like our Sun, becomes a White Dwarf star with the electromagnetic pressure of the electrons refusing to collapse further. This bigger supernova star has enough gravitational force to overcome the electron’s resistance. The electrons can not maintain their orbits and collapse into the nucleus.
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- Neutron pressures and the strong nuclear force are all that is left to keep the star from gravitationally shrinking more. The neutron star becomes a giant atomic nucleus that contains 10^57 sub-atomic particles. The core is 10 kilometers across and made of the densest observable form of matter known.
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- Once the core reaches a density of 10^12 kilograms/meter the protons and electrons themselves become fused into neutrons and neutrinos. A giant firestorm of neutrinos escape.
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- When the density surpasses 10^15 kilograms/meter the neutrons themselves collapse. The density overshoots to 10^18 kilograms/meter as the core collapses further in less than a second. The core bounces, rebounds like a ball hitting a wall and a shock wave travels outward at near the speed of light carrying material away from the core in a giant explosion. The star goes supernova.
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- The entire process takes less than one second reversing over 10 billion years of fusion activity. At the surface of the explosion atoms are hurled against one another with such great force they fuse, taking energy away for the explosion.
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- It is in these collisions that the elements heavier than iron are created. Since your body contains some of these heavier elements, zinc, copper, iodine, you are partly made from the star dust of these supernovae
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------------------------- Compared to hydrogen these elements are still rare:
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------------------------- For every one silicon atom there are 48,000,000,000 atoms.
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-------------------------- There are 630 zinc atoms
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-------------------------- There are 420 copper atoms
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-------------------------- And, there are only 0.41 iodine atoms.
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After the explosion a lone beacon remains, a Pulsar. As the star’s core collapsed it had to spin ever faster in order to “conserve its angular momentum” .
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- If the neutron star , or Pulsar, is rotating 1000 times per second then you on the surface are traveling 62,800 kilometers per second (1,404,796 miles per hour ) The ground below you has the density of 10^18 kilograms per meter. If you weigh 143 pounds, 65 kilograms, on Earth and had this density your dimensions would be 0.000004 meters on a side, 4 thousands of a centimeter. A mere speck weighing 65 kilograms.
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- This rapid rotation causes the star’s magnetic field to compress and intensify to more than a trillion times the strength of Earth’s magnetic field. The spinning magnetic field becomes a monstrous electric generator producing trillions of volts of electromagnetic charge.
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- Particles of equal polarity are shot away from the star’s surface. The magnetic field channels the particles into jets shooting out from the rotating axis. In these jets are streams of electromagnetic energy, with frequencies covering the entire spectrum from radio waves to gamma rays.
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- These beams sweep around space like rotating lighthouse beacon. Here on Earth we might see this beam as a periodic blip, or pulsar, pulsing at one thousand times per second. This spinning neutron star, or black hole, is all that is left after the supernova explosion. The rest is shot out into space. If the magnetic field axis and the rotation axis are aligned you would see no pulse because the jets would always be pointing in the same direction
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- It will take billions of years for our Sun to turn from white-hot, to yellow, then orange, then red before becoming a dark, crystalline cinder in space. The Supernova will spin and radiate away its energy for a million years as it slows down and becomes another dark rock drifting in space.
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So, size matters. The lives of these two stars are totaling controlled by their initial mass. The bigger they are, the faster they die, and the big ones go out with a bang. The bang is Supernova.
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- Other reviews available abut supernovae.
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- 2173 - Today’s expansion rate for the Universe is 49,306 miles per hour per million lightyears distance. The coasting point from expansion decelerating to acceleration occurred about 7 billion years ago.
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- 2149 - Supernovae form blue, super giant stars. This Review list 20 other Reviews about supernovae.
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- 1881 - Supernovae are like snowflakes, everyone is different.
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- 1699 - Supernovae close to home.
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- 1698 - How rare are we in the Universe?
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- 1566 - Supernovae are what we are made of.
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- March 8, 2019 58
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-------------------------- Saturday, March 9, 2019 --------------------------
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