Chapter 8 notes - Fall 2013 Astrophysics of Stars and the...

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Fall 2013 Astrophysics of Stars and the Galaxy 33467, TR 12:00-1:20pm Professor Shirley Ho Come discover how the Milky Way forms, how our own star (aka the Sun) would evolve, how we hunt extra-solar planets, what black holes do in centers of galaxies! The class will be mostly project-based, and we will also learn to data-mine large databases of galactic and extragalactic objects like a modern day astrophysicist!
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Break time 5 mins- Questions/Cirkl!
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Week Month Date Topics book chapters 1 August 27 Overview; Basic Survey of Universe 1 2 September 3 Blackbody, distances, Project brainstorming 2 3 10 Energy Levels, Radiative Energy, HR 2 4 17 Hydrostatic Eq, Virial Theorem, Stars 3 5 24 Stars ; Idea presentation 3 6 October 1 Stellar structure 3 7 8 Stellar Evolution ; Project Presentations 3 8 15 Pulsars, blackholes 4 9 22 Milky Way ; Project Brain-storming 6 10 29 Milky Way; Project idea Presentation 6 11 November 5 Galactic overview, galaxy demographics 6 12 12 AGNs, clusters 6 13 19 special topics 8/9 14 26 Proj discussion - 15 December 3 special topics ; Student Presentations 8/9 16 10 no Fnal -- Syllabus
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ASTR 3730: Fall 2003 Distribution of radio pulsars Can detect pulsars that are much older than the oldest distinct supernova remnants. So most pulsars are not in supernova remnants. More interestingly: not all supernova remnants have pulsars at their center. centered off center
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ASTR 3730: Fall 2003 Together with observations of the distribution and proper motion of radio pulsars across the sky, this suggests that pulsars have velocities that can be as large as 10 3 km s -1 . Much larger than the space velocities of massive stars - suggests neutron stars receive a kick at time of formation.
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ASTR 3730: Fall 2003 Producing neutron star kicks Binding energy of a neutron star is: ~ GM 2 R ~ 5 " 10 53 erg Kinetic energy of a neutron star moving at 1000 km s -1 is: 1 2 Mv 2 = 1.5 " 10 49 erg No energetic problem: small asymmetry in the emission of neutrinos or mass from the supernova would be enough to give the neutron star enough kick energy. Can repeat exercise for momentum as well as energy. Seems plausible, but no definite mechanism is known: • asymmetry in the supernova explosion • irregularities in the progenitor star • …
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ASTR 3730: Fall 2003 Glitches pulse arrival time In some pulsars, the steady spin down is sometimes interrupted by a sudden, almost instantaneous, spin up - a glitch . Thought to arise because the neutron star has a fluid interior which is only weakly coupled to the crust. As the crust is braked, a mismatch in angular velocity develops which is suddenly corrected.
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ASTR 3730: Fall 2003 Binary pulsar In 1974, Russell Hulse and Joe Taylor discovered a pulsar in a close binary system. From analysis of the arrival time of the pulses, they determined that the orbit was eccentric (e = 0.62), with a period of 7.8 hours.
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ASTR 3730: Fall 2003 Observations of this system provide very accurate masses for the stars: M 1 = 1.442 ± 0.003 M sun M 2 = 1.386 ± 0.003 M sun To a very good approximation this is a system of two point masses in orbit around each other.
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