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Incredible Shrinking Stars

Incredible Shrinking Stars. The End States of Stars. White Dwarfs. Earth. White Dwarf. White Dwarf Facts. * Composition: carbon, oxygen * Mass limit < 1.4 M  ( Chandrasekhar Limit ) * Avg mass  0.5 M . Mass, radii  density  1 ton/cm 3. Sirius B (white dwarf). Sirius.

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Incredible Shrinking Stars

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  1. Incredible Shrinking Stars The End States of Stars

  2. White Dwarfs

  3. Earth White Dwarf White Dwarf Facts * Composition: carbon, oxygen * Mass limit < 1.4 M (Chandrasekhar Limit) * Avg mass  0.5 M Mass, radii  density  1 ton/cm3

  4. Sirius B (white dwarf) Sirius Ultimate fate: continuous cooling . . .

  5. Neutron Stars

  6. ~ 10 km Neutron Star: Final state of stellar core in some supernova explosions. • Composition: neutrons • Mass: 1 – 2 M Density ~ 108 ton/cm3

  7. Living on a Neutron Star 1. Your weight is enormous m = your mass M = neutron star mass R = neutrons star radius 150 lbs on Earth  ~ 1013 lbs on a neutron star

  8. 1 meter Splat! 2. Marshmallows become dangerously explosive Energy released equivalent to detonating ~ 10 tons of TNT. Drop marshmallow on neutron star.

  9. * Neutron stars should be rapidly spinning . . . Neutron Star (small diameter, rapid spin) Core, before collapse (large diameter, slow spin)

  10. Slow Fast

  11. * Neutron stars should have strong magnetic fields . . . Field lines become concentrated.

  12. very high small tiny Finding neutron stars 1. They should be hot: T  106 K L = surface area  T4

  13. Conversion of energy of rotation into • em radiation * Rotating magnetic field creates electric field. * Electric field drives electrons along lines of magnetic field. * Electrons radiate – mainly where magnetic field strong.

  14. Rotating neutron star: Pulsar

  15. Crab Nebula Pulsar

  16. Crab pulses X-ray Period = 33 milliseconds (~ 30 rotations per second) Visual Radio

  17. Vela Pulsar: 11.2 pulses/second PSR 1937+21: 640 pulses/second Pulsar Sounds

  18. Black Holes

  19. Mass Limits * White Dwarf: M  1.4 M * Neutron Star: M  2 - 3 M If stellar core should become iron with mass  2 - 3 M . . . Black Hole results!

  20. What is Gravity? Einstein Newton Equivalence Principle

  21. Space is curved – Gravity is a result of geometry! [2-dimensional analog]

  22. Light is affected by gravity . . . Light from distant star follows curvature of space near Sun.

  23. Gravity causes time to slow down . . . Observes ground-floor clock to be slow. Photon loses energy as it moves upward – gravitational redshift.

  24. Top of tower Bottom of tower • e.g., • 2 cycles/sec • (a) 1 cycle/sec • more ticks of clock • (a) fewer ticks of clock

  25. Black hole: infinitely deep ‘puncture’ in space-time.

  26. Singularity: zero volume, infinite density! Schwarzchild Radius (RS) Event Horizon Schwarzchild Black Hole At RS, escape velocity = speed of light

  27. RS (km) = 3M M = mass in units of Sun’s mass e.g., M = 1 M RS = 3  1 = 3 km 6 km The Sun as a black hole

  28. Escape velocity (mi/sec) 7 300 3000 100,000 From surface of: Earth Sun white dwarf neutron star

  29. Tide B. H. Falling into a Black Hole 1. Stretching Less gravity 2. Squeezing More gravity Result: Heating

  30. B. H. As seen by outside observer, time runs slower & slower as person approaches B.H.

  31. Detecting Black Holes * By their effects on other objects. • Strong x-ray source • Only one star detected • Motion of that star  unseen star is very • massive

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