Astronomy 100 Tuesday, Thursday 2:30 - 3:45 pm Tom Burbine [email protected] www.xanga.com/astronomy100OWL assignment (Due Today)ExamOther RoomThings you should knowReview SessionPRS QuestionsPRS question #1Slide 9PRS Question #2Slide 11“Deaths” of StarsSlide 13Slide 14White DwarfsSlide 16Slide 17Electron Degeneracy PressureSlide 19So What Does This MeanOne Interesting ThingWhite Dwarf LimitThe SunNeutron StarHow do you make a neutron star?How do you get a Supernova?Slide 27This stops with IronSlide 29InitiallyThenSlide 32DensityExplosionHow do we know there are neutron stars?PulsarsSlide 37Slide 38Black HolesBlack HoleSlide 41Event HorizonHow do calculate the radius of the Event Horizon?Black Hole SizesSlide 45Can you see a Black Hole?NoEvidenceSlide 49QuestionsAstronomy 100Tuesday, Thursday 2:30 - 3:45 pmTom [email protected]/astronomy100OWL assignment (Due Today)•There is be an OWL assignment due on Tuesday April 5 at 11:59 pm.•There are 15 questions and a perfect score will give you 2 homework points.Exam•40 Questions•Chapters 15, 16, 17, and 18•Some of the questions are taken straight from OWL questionsOther Room•April 7th Goessmann 0020 2:30-3:45 PM Last Names beginning with H, I, J, and KThings you should know•Layers of the Sun•Hydrogen Fusion•Hertzsprung-Russell Diagram•Stellar Classifications•Life Cycle of the Sun•Helium Fusion•CNO cycle•What happens to stars as they “die”Review Session•Wednesday-Review Session–Hasbrouck 134 from 7-8 pm –I will be there at 6 pm if you want to talk to me in a much smaller groupPRS QuestionsPRS question #1•What is approximately the temperature of the plasma in a sunspot?–A) 2,000 K–B) 4,000 K–C) 6,000 K–D) 8,000 K–E) 10,000 KPRS question #1•What is approximately the temperature of the plasma in a sunspot?–A) 2,000 K–B) 4,000 K–C) 6,000 K–D) 8,000 K–E) 10,000 KPRS Question #2•Which of these spectral types have the strongest hydrogen emission lines in their spectra?–A) O–B) B–C) A–D) F–E) GPRS Question #2•Which of these spectral types have the strongest hydrogen emission lines in their spectra?–A) O–B) B–C) A–D) F–E) G“Deaths” of Stars•White Dwarfs•Neutron Stars•Black HolesWhite Dwarfs•White Dwarfs is the core left over when a star can no longer undergo fusion•Very dense–Some have densities of 3 million grams per cubic centimeter–A teaspoon of a white dwarf would weigh as much as an elephantWhite Dwarfs•Some white dwarfs have the same mass as the Sun but slightly bigger than the Earth•200,000 times as dense as the earthWhite Dwarfs•Collapsing due to gravity•The collapse is stopped by electron degeneracy pressureElectron Degeneracy Pressure•No two electrons can occupy the same quantum stateElectron Degeneracy Pressure•As electrons are moved closer together•Their momentum (velocity) increases•Due to Heisenberg Uncertainty PrincipleSo What Does This Mean•Electron Degeneracy Pressure balances the gravitational force due to gravity in white dwarfsOne Interesting Thing•More massive white dwarfs are smallerWhite Dwarf Limit•The mass of a White Dwarf can not exceed approximately 1.4 Solar Masses•Called the Chandrasekhar Limit•Electrons would have velocities greater than the speed of lightThe Sun•Will end up as a White DwarfNeutron Star•Neutron stars are usually 10 kilometers acroos•But more massive than the Sun•Made almost entirely of neutrons•Electrons and protons have fused togetherHow do you make a neutron star?•Remnant of a SupernovaHow do you get a Supernova?•A high-mass star keeps on fusing elements into ones with larger atomic masses•Is now a Red Supergiant•Energy keeps on being released since the mass of the new nucleus is less than the original onesThis stops with Iron•Fusion of Iron with another element does not release energy•Fission of Iron with another element does not release energy•So you keep on making IronInitially •Gravity keeps on pulling the core together•The core keeps on shrinking•Electron degeneracy keeps the core together for awhileThen•The iron core becomes too massive and collapses•The iron core becomes neutrons when protons and electrons fuse togetherDensity•You could take everybody on Earth and cram them into a volume the size of sugar cubeExplosion•The collapse of the core releases a huge amount of energy since the rest of the star collapses and then bounces off the neutron core•1044-46 Joules•Annual energy generation of Sun is 1034 JoulesHow do we know there are neutron stars?•The identification of Pulsars•Pulsars give out pulses of radio waves at precise intervalsPulsars•Pulsars were found at the center of supernovae remnantsPulsars•Pulsars were interpreted as rotating neutron stars•Only neutron stars could rotate that fast•Strong magnetic fields can beam radiation outBlack Holes•If a collapsing stellar core has a mass greater than 3 solar masses,•It becomes a black holeBlack Hole•After a supernova if all the outer mass of the star is not blown off•The mass falls back on the neutron star•The gravity causes the neutron star to keep contractingBlack Hole•A black hole is a region where nothing can escape, even light.Event Horizon•Event Horizon is the boundary between the inside and outside of the Black Hole•Within the Event Horizon, the escape velocity is greater than the speed of light•Nothing can escape once it enters the Event HorizonHow do calculate the radius of the Event Horizon?•It is called the Schwarzschild Radius•Radius = 2GM/c2 •This is a variation of the escape velocity formula•Escape velocity = square root (2GMplanet/Rplanet)Black Hole Sizes•A Black Hole with the mass of the Earth would have a radius of 0.009 meters•A Black Hole with the mass of the Sun would have a radius of 3 kilometersCan you see a Black Hole?No•Black Holes do not emit any light•So you must see them indirectly•You need to see the effects of their gravityEvidence•The white area is the core of a Galaxy•Inside the core there is a brown spiral-shaped disk. •It weighs a hundred thousand times as much as our Sun.Evidence•Because it is rotating we can measure its radii and speed, and hence determine its mass. •This object is about as large as our solar system, but weighs 1,200,000,000 times as much as our sun. •Gravity is about one million times as strong as on the sun.