Chapter 22 - Physics1902 NeutronStars,BlackHolesand...

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1 Physics 1902 Neutron Stars, Black Holes and  other Weirdos Lecture W9.b Chapter 22
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2 Neutron Stars The result of the type II SN is a highly compressed core and the exploding remnants The core is essentially at nuclear densities and is supported by neutron degeneracy pressure It is mostly neutrons
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3 What should this look like? 1) it should be very small (about 20 km) 2) it should be very dense (100,000,000 tonnes per cc) 3) It should be rotating very fast As the core collapsed, its rotational speed needs to increase to conserve angular momentum 4)It should have a strong magnetic field The magnetic field lines are compressed along with the core
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4 Discovery of a neutron star Graduate Student (Jocelyn Bell) at Cambridge was observing radio signals from space She observed a signal that was pulsing
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5 Implications of the discovery The fast rise of the signals limits the size of the object (each pulse was ~ 10 ms long) Object cannot be more than a few light-ms in size The regular spacing suggests rotation 1500 now known in the Milky Way Some are more regular in their frequency than the best atomic clocks Jocelyn’s supervisor collects Nobel prize for identifying neutron stars
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6 And we can even listen to pulsars
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7
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8 Back to the Crab Nebula The Crab is our well studied SN remnant Can we see evidence for a pulsar at its core?
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9
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10 Central Part Of Crab
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11 Crab on and off states
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12 Light curve for Crab
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13 Observations on Crab We see a pulsar flash every 30 ms The neutron star is rotating ~ 30 times per second The period is not absolutely stable – it is slowing down Energy from slowdown is sufficient to power the observed remnant Energy from ‘synchrotron emission’ gives very strong radio signal We think the radiation is narrowly peaked in direction We only see pulsars that point at us in some part of their rotation
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14 Neutron stars and gamma rays  Neutron stars are also seen in gamma rays
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15 Gemina Pulsar Crab Pulsar Crab pulses too fast to resolve
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Chapter 22 - Physics1902 NeutronStars,BlackHolesand...

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