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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