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The Death Of a Star

The Death Of a Star. Ask not for whom the bell tolls, it tolls for thee. How do we “know” stars die?. HR Diagrams reveal different types of stars. How did they get there? Physics tells us how stars work. Luminosity depends on mass (L:M 4 ) (Gas)

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The Death Of a Star

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  1. The Death Of a Star Ask not for whom the bell tolls, it tolls for thee

  2. How do we “know” stars die? • HR Diagrams reveal different types of stars. • How did they get there? • Physics tells us how stars work. • Luminosity depends on mass (L:M4) (Gas) • Fusion principles (4 H  1 He) tell us the rate stars use energy. (kinda like MPG on a car.) • Stars will run out of fuel. (the dial goes to “E”)

  3. Every star fights a “battle”. • Gravity force pulling the star together. • Fusion “force” pushing the star apart. • Most stars find a balance. • Some stars are never balanced: • Cephids pulse as they growlarger and smaller. Gravity Fusion

  4. Cepheus

  5. A star’s fate is chosen at birth • The outcome of the battle is determined by gravity and gravity means Mass

  6. Three paths

  7. Small Stars • Small stars last longer (don’t consume fuel as quickly) • Main sequence on HR diagrams. • “Burn” hydrogen for most of their lifetime.

  8. Red Giants • As star runs out of hydrogen, the core cools • Gravity starts to “win” --> shrinkage in core. • Increased “pressure” starts Helium fusion • 150 Million K • Carbon & Oxygen Products • Hotter temperature makes outer part of star expand yet…. • Expanded surface is actually “cooler” so appears red

  9. Red Giants • Stars less than 1.4 Solar Masses • Gravity is weak • Outer layers eventually “puff off” - not enough gravity • Planetary nebula forms from gas • White dwarf remains

  10. If it’s a cloud, why does it look like a ring?

  11. Cat’s Eye: Another Planetary Nebula

  12. White Dwarfs • Carbon/Oxygen • Matter is compressed • One teaspoon = a pickup truck • Electron/quantum pressures balance gravity • Very Hot : 30,000K to 200,000 K • Slowly Cool to Black Dwarfs • So slow, none exist yet. • Except this guy 

  13. White Dwarfs

  14. Red Supergiants • Stars more than 1.4 Solar Masses • Gravitational Core Energy Reaches 150 Million K • Carbon turns to Mg, O, & N • With enough mass, even heavier elements fused • At each step, less and less energy yielded --> shorter duration • Star keeps getting bigger! • Iron is the end of the road….

  15. The most famous S-G

  16. Fusion Layers in a Supergiant

  17. Why Stop at Iron??

  18. Review Mass • ______ determines the fate of a star. • The two forces acting on a star are ____ and _____ • When a star reaches the end of its life it begins to fuse ______ and it ______. • When fusion stops a typical star will produce a __ and become a ______ _____. • Even the largest stars can’t fuse elements heavier than _____. gravity fusion helium swells planetary nebula white dwarf iron

  19. The party is over… • Once iron is in the core, outwards pressure ceases • Core collapses at 1/4 the speed of light & takes about 1/10 of a second • Collapse of the core to about 100 km across • Outer layers “bounce” of the solid core • Releases 100x the energy of our sun produces in it’s lifetime -- in 1/10 of a second!!!

  20. A supernova • Note the before / after differences • 1987A

  21. After the party… • Lot’s of neutrons hanging out during this explosion • Neutrons “hook - up” with lighter elements making heavy elements: • Calcium, Gold, Zinc, Uranium, etc… • Forget Hollywood ….. We are all stars!!!

  22. Aftermath: • After a supernova explosion you can wind up several possibilities • Nebula & Neutron Star • Nebula & Pulsar • Black Hole

  23. Nebula • Clouds of material left from the explosion • The “Primordial Goo” for new stars, planets, & people!

  24. Supernova 1987 • Very complicated structure • Nearby star affecting the cloud

  25. Our new neighbors?

  26. Neutron star • Forms if the remaining core is between 1.4 and 3 times the sun’s mass • All this mass in the size of Schaumburg! • One teaspoon > The Sears Tower • All available space in the atom (which is 99.9999% space) is removed.

  27. Neutron Star

  28. Pulsar • Neutron star that spins. • Spinning magnetic field channels radiating energy into beams. • If this beam isn’t always pointing at us - it flashes like a lighthouse. • First Pulsar was mistaken as alien communication

  29. A Pulsar

  30. Black Holes • Remaining Core is more than 3x the sun. • Gravity overcomes everything, neutrons vanish • Matter in the core overlaps : a singularity • Gravity prevents light from escaping.--> Black Hole • Closest light can get without being trapped: “Event Horizon” • 3 S.M star = 55km E.H. (Chicago?) • Earth as a black hole? Compress it into a marble!

  31. Finding Black Holes • May pull matter off a nearby star - Accretion Disk X-Rays • Immense mass in the center of galaxies

  32. A trip to a black hole • Pretty Short • Difference in gravity between your head and feet literally pull you apart. • Once you hit the E.H. you aren’t coming back. • Everything you are is crushed into a single point - you no longer exist • No one would see you enter the Black Hole because time stands still at the edge.

  33. Black Holes - Expert Testimony Black Holes –More Expert Testimony

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