AST- 105 1st EditionLecture 18Outline of Last LectureI. Open Star ClusterII. Globular Star ClusterIII. Star Cluster AgesIV. The EquinoxesOutline of Current Lecture I. SupernovaII. Neutron StarsIII. Pulsar ModelCurrent Lecture I. Supernovaa. Supernova- death of a massive stari. Gravity overcomes outward electron pressure in iron core, causing rapid collapse.ii. Electrons and protons combine to form neutrons.iii. Neutrinos (very low mass particles) are produced.iv. Pulse of neutrinos is emitted.v. Neutron pressure stops collapse when core is 20 km (12 mi) across because the pressure is then balancing the gravity in the core. b. The Supernova Blasti. Energy released by core collapse causes shock wave to travel outii. Rest of the star explodes outwardiii. Elements heavier than iron are produced in the blast1. Elements heavier than H and He are produced in massive stars.2. Supernova explosions return these elements to interstellar gas.a. Stars, planets, and life form from gas ejected by supernova.II. Neutron Starsa. Neutron Stars- ultra-collapsed stellar core, produced by supernovai. Mass is greater than 1.5 Mʘii. Radius = 10 km = 6 milesiii. Made of tightly packed neutronsiv. Young neutron stars are found in supernova remnents1. Ex. Crab Nebulaa. Rapidly expanding hot gasb. Can emit all forms of EM radiation: radio to gamma rays III. Pulsar Modela. Pulsar Model- magnetized, rapidly rotating neutron star. i. Magnetic and rotation axes not alignedii. Radiation beamed along magnetic axis1. We see a flash when beam sweeps past us…this is known as the “Lighthouse Effect”iii. Why is the rotation so fast?1. Conservation of angular momentum- “Ice Skater Effect”a. Original star had moderate rotationb. As core collapsed, spin rate greatly increasedc. Fastest pulsar spin rate: 700 per sec = 42,000
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