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ISP Chapter 13

# ISP Chapter 13 - Chapter 13 WHITE DWARFS AND NEUTRON STARS...

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Chapter 13 WHITE DWARFS AND NEUTRON STARS White dwarfs are the cores of dead stars Electron degeneracy pressure supports them against gravity They become dimmer and redder as they cool off o Small: faint, get fainter o Hot: but cools steadily with time About the size of the earth ORGIN OF DEGENERACY PRESSURE Exclusion principle: two electrons in the same position cannot have the same momentum o Electrons (or protons and neutrons) can’t be pushed together past a certain limit Uncertainty principle: an electron’s momentum and position cannot both be specified with infinite precision o If the space an electron can be is very small, its momentum can be very LARGE ALSO true for protons and neutrons ? What happens to a white dwarf when you add mass to it? -gravity squeezes the electrons into a smaller space White dwarfs shrink when you add mass to them ? What happens to the speeds of electrons in a white dwarf when you add mass to it? -the electrons speed up because their average momentum must increase ? Is there a limit to how much mass you can add to a white dwarf? -Yes, because the electrons can’t speed up to greater than the speed of light When electron speeds in a white dwarf approach speed of light, electron degeneracy pressure can no longer support it WHAT CAN HAPPEN TO A WHITE DWARF INA CLOSE BINARY SYSTEM? Matter flows from subgiant to main sequence star And then eventually it becomes white dwarf Infalling matter forms an accretion disk around white dwarf Friction in the disk makes its gas hot, causing it to glow Friction also removes angular momentum from inner regions of disk, allowing gas to drop onto white dwarf ? What happens to a white dwarf when it accretes enough matter to reach the 1.4 Msun limit?

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