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ASTRONOMY

ASTRONOMY. Chapter 30 Pulsars and Neutron Stars. Formation of a Neutron Star. In the iron core of a high-mass star: Iron nuclei break into He nuclei, protons, and neutrons Energy is carried out and the pressure drops The core collapses.

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ASTRONOMY

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  1. ASTRONOMY Chapter 30 Pulsars and Neutron Stars

  2. Formation of a Neutron Star • In the iron core of a high-mass star: • Iron nuclei break into He nuclei, protons, and neutrons • Energy is carried out and the pressure drops • The core collapses. • Electrons are squeezed into the nucleus where they react with protons • Neutrons and neutrinos are formed • Neutrinos escape taking more energy

  3. Formation of a Neutron Star • After the explosion, the remaining mass can be from a few tenths M˳ to 3 M˳ • Core collapses until neutron degeneracy balances the gravity and the star becomes stable. • 1 teaspoon would weigh 1 billion tons on earth

  4. Comparison • A white dwarf packs the mass of the sun into the size of Earth. • A neutron star packs the mass of 2 suns into a 20 km diameter.

  5. Pulsars • Discovered in 1967 • Search has found that they are located in our galaxy • Periods range from thousandths of a second to four seconds. • Questions: • What are they? • What makes them tick”?

  6. The Lighthouse Model

  7. Crab Nebula “Proof” • A pulsar was discovered at the center of the Crab Nebula • Its period was found to be 0.033s • It is rotating at 30 revolutions per second • This speed would tear apart a white dwarf. • This pulsar radiates in all parts of the spectrum • Fastest known pulsar – the millisecond pulsar – spins at 642 rev/s

  8. Crab Nebula “Proof”

  9. Binary Pulsars • A pulsar in a binary system can exhibit a Doppler shift as it orbits its companion. • Relativity predicts gravitational waves from binary pulsars. • None have been detected so far.

  10. X-ray Binaries • Orbiting X-ray telescopes have detected some stars that pulse in x-rays • This is probably due to mass from the companion star being funneled to an accretion disk around the neutron star. • This gas heats up and emits x-rays.

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