PHY121 Ch 11 Notes

PHY121 Ch 11 Notes - Astronomy Chapter 11: Neutron Stars...

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Neutron Star A supernova explosion of an M > 8 M sun star blows away its outer layers The central core will collapse into a compact object of a few M sun core can’t support itself as a white dwarf if mass is greater than 1.4 (Chandrasekhar limit) If mass between 1.4 and 3 M o – the pressure becomes so high that electrons and protons combine to form stable neutrons throughout the object; can halt contraction and form neutron star A neutron star is supported by the pressure of the degenerate neutrons. Theory predicts that a neutron star should spin very fast because it conserves angular momentum as it contracts, and have a powerful magnetic field. Typical size: R ~ 10 km Mass: M ~ 1.4 – 3 M sun Density: ρ ~ 10 14 g/cm 3 Piece of neutron star matter of the size of a sugar cube has a mass of 100 million tons! Remnant of supernova observed in AD 1054 – the Crab Pulsar Pulsars rapidly pulsing radio sources, were discovered in 1967. Angular momentum conservation – collapsing stellar core spins up to periods of a few milliseconds Magnetic field lines trapped inside original star become more dense producing fields up to B ~ 10 9 – 10 15 G (10 12 times the sun’s magnetic field) Rapidly pulsed (radio, optical, and X-ray) emission from some object interpreted as spin period of neutron stars The lighthouse model explains pulsars as spinning neutron stars that emit beams of radiation from their magnetic poles. As they spin, they sweep the beams around the sky like a lighthouse
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PHY121 Ch 11 Notes - Astronomy Chapter 11: Neutron Stars...

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