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Neutron Star Gravitational Crush • The balance point to maintain degenerate matter is 1.4 M. • When the mass of the core is greater than 1.4 M, electrons cannot support the gravitational force. • This is the Chandrasekar limit: beyond that it’s supernova. white dwarf supernova Neutrons • Degenerate matter is already compressed, but there are both electrons and nuclei. • With the pressure and temperature electrons can fuse with protons into neutrons. electron proton nucleus neutron neutrons only fewer particles Neutron Core • The packed neutrons remain and become a neutron star. – Very hot: 200 billion K – Very small: 10 - 30 km, the size of De Kalb county – Very dense: 100 million tons per cm3 Surface Gravity • Surface gravity is proportional to the mass divided by the radius squared. – Mns = M , about 106 Mearth. – Rns = 0.003 Rearth. – The surface gravity, gns = 1011 gearth. X-rays • The surface gravity creates tremendous accelerations. – Photons from accelerating electrons – X-rays from high energy • X-ray telescopes in orbit can spot neutron stars in supernova remnants. Pulsars • Neutron stars create very large magnetic fields. – Increased spin from collapse – Spin up to 30 Hz (30 times per second) • These pulsars can be observed as repeating flashes of light as the magnetic poles point towards us. X-ray Pulsars • Pulsars also emit x-rays. – Appear to blink as pulsar spins – Time between blinks = period of the pulsar crab nebula off crab nebula on