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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.
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.
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
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.
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.
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
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
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.
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!
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.
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!
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.
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.
Works Cited1. Wittkowski, M.; Hauschildt; Arroyo-Torres, B.; Marcaide, J.M. (5 April 2012). "Fundamental properties and atmospheric structure of the red supergiant VY CMa based on VLTI/AMBER spectro-interferometry". Astronomy & Astrophysics 540: L12.2. Giacobbe, F. W. (2005). "How a Type II Supernova Explodes". Electronic Journal of Theoretical Physics 2 (6): 30–383. http://www.efda.org/fusion/how-fusion-works/4. http://www.time.com/time/magazine/article/0,9 171,836188,00.html