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Lecture 3

EPSC201 Lecture 3 Notes.doc

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Earth & Planetary Sciences
EPSC 201
Anthony Williams- Jones

EPSC201 - Lecture 3 Notes Universe – Big Bang: The universe initially had infinite energy. Energy converted to mass, temperature decreased. Universe ex- panded, and temperature decreased further. • 2 up quarks + 1 down quark = proton 2 down quark + 1 up quark = neutron • • Proton + neutron = hydrogen nucleus Energy throughout the early universe was being bounced around, and made it impossible to discern any- thing. It was very dense and hot. Impossible to see before. 379,000 years after Big Bang. From this point on, we can observe the universe. At 6000 degrees, it was cold enough to start observing. At about 379 years after the big bang, the background scattering effectively stopped. Atoms have formed and matter has spread out. The universe is observable. Cannot observe before 379 years due to energy scattering. This all occurred when the uni- verse was about 6000 degrees Kelvin. Now the temperature is 2.75 degrees Kelvin. Things have cooled off. Bell lab scientists observed this radiation in the sixties. Scientists calculated that there would be a specif- ic background radiation at 2.75 de- grees, and if the background radiation is measured from space, it is found to be the same wavelength. Black Body Radiation – absorbs all forms of radiation and reemits all forms too. The early universe was nearly a perfect blackbody; all radia- tion was re emitted and absorbed. At 379,000 years after Big Bang, the universe was heterogeneous. Matter was already clumped throughout the universe, which gives rise to hot and cold spots. The first stars were massive, around a million years after the Big Bang. There were clouds of material, largely of hydrogen and small elements, spread throughout the universe. These patches drag in more matter, and gravita- tional collapse occurs. This is how stars are made. Stars shine because they are emitting energy. Once they reach 10 million degrees, nuclear fusion occurs. Deuterium is quickly formed, and it transforms into helium. The formation of helium releases a lot of ener- gy. The core temperature of our sun is about 15 million degrees, the surface is 6000 degrees. Star forma- tion requires that you have enough mass to reach the threshold energy, for nucleosynthesis to occur. If there is not enough mass present, the star will not be formed, it won’t be hot enough. Nucleosynthesis of helium is why stars emit energy. As the temperature increases, heavier elements are formed. In theory, a billion degrees can be reached before the star explodes. If the cloud is large enough, many stars will be formed. As mat- ter is dragged inwards, it starts to spin (true for galaxy and star formation). Most stars and galaxies spin. At the core of the galaxy lies the ma- jority of the mass. The more it spins, the tighter ring it will form. Slow spinning galaxies have wider arms. Our galaxy is 90,000 light years across. Our galaxy does spin; every 250 million years our galaxy completes a rotation. At the center of our universe, there is a black hole. Black hole – an object that is so massive, that nothing can escape it (not light or mass). That’s why they don’t emit light. We cannot see black holes for this reason, but we can de- tect them by gravitation field distortions. Our star was made roughly three and a half billion years ago, and has roughly the same time to live. Our star is middle aged. It is also a 2nd or 3rd genera- tion star. It is in equilibrium where gravity is pulling it together, and fusion is exploding it outward. It’s com- position is much different then a 1st generation star, which are much older. The material in the outside of the star has an easier time to overcome gravity and explode outward to become a red giant when nuclear fusion starts to consume most of the
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