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Star Deaths

Star Deaths. Mass matters!. Star Deaths. Stars die when fusion reactions stop (still contains heat energy) Mass at the time of death determines the form of the corpse Stars lose mass before their corpse forms (winds, explosions) Corpses last “ forever ”. Mass (at death)

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Star Deaths

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  1. Star Deaths Mass matters!

  2. Star Deaths • Stars die when fusion reactions stop (still contains heat energy) • Mass at the time of death determines the form of the corpse • Stars lose mass before their corpse forms (winds, explosions) • Corpses last “forever”

  3. Mass (at death) > 0.08 solar mass 0.08 to 1.4 solar masses 1.4 to 3 solar masses > 3 solar masses Corpse Brown dwarf White dwarf Neutron star Black hole! Star Deaths

  4. White Dwarf • Mass: bit less than the sun’s • Size: about that of the earth • Density: about 109 kg/m3 • Made of: electron gas (degenerate-greater mass, smaller size) • Shines: by outflow of stored heat

  5. Neutron Star • Mass: around 2 solar masses • Size: about 10 km (city!) • Density: about 1017 kg/m3(atom’s nucleus!) • Made of: neutron gas (degenerate) • Made in: supernova explosions

  6. Black Holes • Mass: ANY; expect 3 to 10 solar masses from normal star death • Size: Schwarzschild radius-a few km(about 3 km for sun; directly proportional to mass) • Escape speed: equal to or greater than speed of light • Inside: mass has zero volume, infinite density—the singularity

  7. Black Holes • Made of: warped spacetime (essentially permanent!) • Time is “frozen” at the Schwarzschild radius (to outside observer); never sees objects “fall in” • As black holes gain mass, they grow in size (can never shrink)

  8. Black Holes • Measure mass by visible orbiting body (Newton’s version of Kepler’s 3rd) • Most likely found in binary stars(black hole + regular massive star) • Are not cosmic vacuum cleaners (but don’t get up close!)

  9. Black Holes: X-rays • Matter from companion star falls into an small accretion disk (about 10 km) around the black hole • Disk heats up to about 10,000,000 K (conversion of gravitational energy) • Opaque material of disk emits x-rays (blackbody) • Search in binary x-ray sources

  10. Supernovas! • Peak at 10 billion solar luminosities • Lifetime about a few months • Total energy about 1046 joules (99% as neutrinos) • Blows off a few solar masses of material at thousands km/s (supernova remnant)

  11. Supernovas! • One type: Old massive star (about 10 solar masses) with unstable iron core • Core collapses in about 1 second! • Implosion releases gravitational energy, high temps for fusion reactions • Fuses elements heavier than iron; blasted into space

  12. Neutron Stars: Pulsars! • Supernova core collapse makes neutron star (usually!) • Pulsars usually found near center of supernova remnants • Pulsars emit very short pulses (ms) at very regular intervals • Rapidly-rotating, highly-magnetic neutron stars are pulsars

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