College 9 - Stellar remnants
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White dwarfs
LB 257 - 259
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neutron stars
LB 259 - 262
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Black holes
LB 262 - 268
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White dwarfs
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as they are compact and hot
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radius ~1 % solar, density 106 g/cm3 (average density sun 1g/cm3)
White dwarfs are stellar remnants of low to intermediatemass stars – 90% of the stars end as white dwarfs
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internal pressure due to degenerate electron gas
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core mostly He or C and O, outer layer may also contain H
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Chandrasekhar limit: 1.43 solar masses. Higher mass white
dwarfs turn into neutron stars through neutronization:
Ultimately cool to black dwarfs, crystallization of C-rich
dwarfs will yield the Universe diamonds
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http://en.wikipedia.org/wiki/Sirius
The image of Sirius A and Sirius B taken by
the Hubble Space Telescope. The white
dwarf can be seen to the lower left.[82] The
diffraction spikes and concentric rings are
instrumental effects.
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Neutron stars and pulsars
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1.43 solar mass < M < 3 solar mass
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radius ~ 10 km, density ~ 1014 g/cm3
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(mass 1cm3 = all humans on earth)
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outer crust: solid matter composed of nuclei (iron) and
free electrons
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inner structure not clear: quarks?
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A pulsar:
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a fast rotating neutron star (1ms – 10 sec) with dipolar
magnetic field that is inclined with respect to the axis of rotation
of the neutron star. Typical magnetic field ~ 1014 G.
Pulsars emit pulses of synchrotron radiation.
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Black holes
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Even light can not escape.
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For a proper description general relativity is needed
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GR treats 'gravity' as a distortion in space-time.
Three properties: mass, charge, spin
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A classical (incorrect...) approach:
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