Lives and Deaths of Stars Notes 8/29/16 - 9/2/16
Lives and Deaths of Stars Notes 8/29/16 - 9/2/16 AST 309N
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This 3 page Class Notes was uploaded by Emma Huff on Friday September 2, 2016. The Class Notes belongs to AST 309N at University of Texas at Austin taught by Harriet Dinerstein in Fall 2016. Since its upload, it has received 7 views. For similar materials see Lives and Deaths of Stars in Astronomy at University of Texas at Austin.
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Date Created: 09/02/16
Lives and Deaths of Stars 8/29/16 - 9/2/16 Class Notes 8/30/16: - Atomic Number: the number of protons in the nucleus of an atom of an element - Atomic Mass Number: the number of protons + the number of neutrons in the nucleus of an atom of an element - Isotope: variations of an element where the nucleus has the same number of protons but different numbers of neutrons - The protons in the nucleus hold together and don't repel because nuclear force overcomes electrical force. - The universe is 99.9% hydrogen and helium. - Atoms are made in the extremely hot insides of stars, where particles are moving so fast that they don’t have time to repel each other. - The fundamental forces of nature (from weakest to strongest): gravity, electromagnetism, weak nuclear force, and strong nuclear force. These cannot be stopped. - Applied forces such as pushing and viscous forces are called contact forces; they can be turned on and off. They can be stopped. - Electromagnetic forces are associated with chemical reactions, whereas nuclear forces are associated with nuclear reactions. - In science, force, energy, and momentum have different meanings and different properties. “Amount” Aspect “Direction” Aspect Energy Yes No Force Yes Yes Momentum Yes Yes - Momentum (p): p = m x v is proportional to v; changing the momentum of a body requires application of a force - Energy (Joules): 1 Calorie = 4.18 Joules; 1 erg = 10^7 Joules; 1 electron volt = 1.6 x 10^-19 Joules = 160 zeptoJoules - Conservation of energy: the conversion or transfer of energy means that energy has different forms - Potential Energy: the energy of position - Gravitational Potential Energy: the energy available if an object is allowed to fall under gravity; depends on an object’s mass, acceleration of gravity, and height form which it falls - Kinetic Energy: the energy of movement - K.E. = .5m x v^2 is proportional to v^2 - temperature is a measure of average kinetic energy - K.E. can be macroscopic (bulk) energy or microscopic (internal) motion - Thermal Energy: the total energy of all particles - Given different forms of energy and their ability to to transfer, energy’s total is constant. - Rest-Mass Energy: energy is stored in matter itself; it would be released if matter were converted into energy; this is the basis of E = m x c^2 Class Notes 9/1/16: - Chemical Composition: proportions of different elements in a substance - Conversion of Energy: when one type of energy is converted into another - Rest-Mass Energy: energy that is stored in the form of matter - The 2 Types of Nuclear Reactions - fission: when big nuclei break apart into smaller nuclei (radioactive decay) - fusion: when smaller nuclei join together to make a bigger nucleus; this is the energy source for the sun - Nuclear fusion only happens in the inner 1/4th of the sun. - Nuclei repel because of their positive electromagnetic charges. - In order for nuclear fusion to occur, the nuclei must have enough kinetic energy to overcome repulsion. - The contracting proto-sun heated up due to the conversion of gravitational potential energy into kinetic and thermal energy. - The sun’s center became hot and dense enough for hydrogen to begin fusing into helium. - Fusion provided the ongoing energy source to maintain temperature and pressure. - Then, the sun stabilized as a Main Sequence star. - Thermal Pressure: the force that provides balance against gravity in a star; it is directly proportionate to temperature - How Energy Gets Out of the Sun: - radiation: Energy travels as photons, which interact with particles by being absorbed and emitted. With each interaction, the photon changes direction (random walk) and loses energy. It takes 100s of 1000s of years for a photon to travel out from the core of the sun. - convection: Photons are absorbed by an opaque layer that blocks their transport. This is when a convection current occurs. Energy is carried upward with material as it rises. Granules that we see on the surface of the sun are the tops of hot gas bubbles. Convection moves mass as well as energy, so it can potentially change composition. - In the sun’s core (inner 25%), energy is created by nuclear fusion. - In the sun’s radiative zone (inner 70%), energy is transported by photons. - In the sun’s convective zone (outer 30%), energy is transported by convection. - The sun sometimes “shivers”, meaning that bumps on its surface swell and flatten.
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