week 7 lecture notes
week 7 lecture notes ASTR 121
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This 4 page Class Notes was uploaded by Anisa sudra on Saturday May 16, 2015. The Class Notes belongs to ASTR 121 at University of Oregon taught by Scott Fisher in Spring 2015. Since its upload, it has received 98 views. For similar materials see ASTR 121 The Solar System in Astronomy at University of Oregon.
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Date Created: 05/16/15
WEEK 7 51615 140 PM EXAM 2 FRIDAY MAY 22 101 A closer look at the sun GOALS 0 Why does the sun shine What is the sun s structure WHY DOES THE SUN SHINE the amount of energy that the sun gives off each second Is the sun on fire No If it were Chemical energy contentluminosity 10000 years Is the sun contracting No If it were Gravitational potential energyluminosity 25 million years The sun is powered by nuclear energy Nuclear potential energy coreluminosity 10 billion years 0 only nuclear reactions can provide energy for long enough a flow of charged particles from the surface of the sun There is a wind of these particles coming off of the sun this is what protects us from the solar wind Without the magnetic field we would have MUCH stronger effects from the sun on Earth outermost layer of solar atmosphere 0 1 million K no one knows why it is this temp visible surface of the sun 0 600 K o the surface of the sun appears and is granular where energy is generated by nuclear fusion 0 15 million K 103 The SunEarth Connection GOALS o What causes solar activity What causes solar activity 0 Magnetic field of the sun Solar activity is like weather on Earth 0 Sunspots 0 Solar flares 0 Solar prominences 0 Areas on the photosphere that are cooler than other parts of the sun s surface 400 K 0 These regions have strong magnetic fields 0 Loops of bright gas often connect sunspot pairs 0 Caused by magnetic activity that sends bursts of x rays and charged particles into space 0 Magnetic activity send bursts of energetic charged particles out through the solar system 0 1112 year cycle that has something to do with the winding and twisting of the sun s magnetic field 0 Where activity rises and falls Chapter 13 o All of the elements on the periodic table except for H He Li is star stuff Once Hydrogen fusion slows down it ends with a pulse that ejects the H and He into space The core led behind becomes a white dwarf The White Dwarf illuminates the material causing it to glow as a planetary nebula White Dwarfs o The exposed Carbon core of a dead lowmass star that shed its outer layers in a planetary nebula 0 Electron degeneracy pressure supports a white dwarf against gravity 0 Sirius is also known as the Dog Star 0 The exposed Carbon core of a dead lowmass star that shed its outer layers in a planetary nebula 0 Electron degeneracy pressure supports a white dwarf against gravity A white dwarf is about the same size as Earth they are VERY dense o 05 14 MSun packed into a sphere the size of the Earth 0 300000 Earth masses in the same volume 0 a teaspoon of white dwarf maaer would weigh several tons on Earth pressure force per unit area on container When you remove the heat source gas cools down pressure drops gas gets more dense Pressure provided by electrons due to the effects of quantum mechanics A white dwarf that is supported by electron degeneracy is at almost the minimum volume that an amount of mass can be compressed into all the electrons are almost touchingquot All available energy levels below a certain value are full so many highenergy hot electrons cannot cool down lose energy o they stay hot even if there is no heat source Those hot electrons provide the pressure that supports White Dwarf Quantum mechanics says that electrons that are very close to each other cannot have the same energy that means electrons can only get so close to each other and no closer Adding mass to a white dwarf increases its gravity forcing electrons and nuclei into a smaller and smaller space Is there a limit to how much you can shrink a white dwarf YES The Chandrasekhar Limit is when a white dwarf has a mass of 14 mes the mass of the Sun 14 Msun At this point the inward pull of gravity overwhelms outward pressure of electron degeneracy and the white dwarf collapses and goes supernova Collapse raises WD core temperature rapidly above 600 million K runaway carbon fusion begins and WD explodes Such an exploding WD called a white dwarf supernova A WD supernova attains a luminosity of 10 billion Suns 9Complete explosion of WD nothing led behind
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