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Transcript
The Life Cycles of Stars Twinkle, Twinkle, Little Star ... How I Wonder What You Are ... Stars have • Different colors Which indicate different temperatures The hotter a star is, the faster it burns its life away. Stellar Nursery: A NEBULA Space is filled with the stuff to make stars. Stars start from clouds Clouds provide the gas and dust from which stars form. But not this kind of dust Rather: Irregular Grains Of Carbon or Silicon Collapse to Protostar Stars begin with slow accumulation of gas and dust. • Gravitational attraction of Clumps attracts more material. • Contraction causes Temperature and Pressure to slowly increase. Nuclear Fusion ! At 15 million degrees Celsius in the center of the star, fusion ignites ! H + H He + energy A Balancing Act Energy released from nuclear fusion counteracts inward force of gravity. Throughout its life, these two forces determine the stages of a star’s life. ***MAIN SEQUENCE STAR*** New Stars are not quiet ! Expulsion of gas from a young binary star system All Types of Stars Recall Stars have Different colors which indicate different temperatures All Types of Stars Reprise: the Life Cycle red supergiant main sequence red giant Low-med mass High mass protostars collapses nebula supernova pulsar white dwarf black dwarf Sun-like Stars blackhole Massive Stars A Red Giant You Know BETELGUESE in the constellation ORION The Beginning of the End: Red Giants After Hydrogen is exhausted in core ... Energy released from nuclear fusion counter-acts inward force of gravity. • Core collapses, Kinetic energy of collapse converted into heat. This heat expands the outer layers. • Meanwhile, as core collapses, Increasing Temperature and Pressure ... More Fusion ! At 100 million degrees Celsius, Helium fuses: He + He + He Carbon + ENERGY Energy sustains the expanded outer layers of the Red Giant The end for solar type stars After Helium exhausted, outer layers of star expelled WHITE DWARF in the centre New Planetary Nebulae Are Made White dwarfs At center of Planetary Nebula lies a White Dwarf: • Size of the Earth with Mass of the Sun “A ton per teaspoon” • Inward force of gravity balanced by repulsive force of electrons. END OF A LOW MASS STAR: White Dwarf cools and becomes a Black Dwarf The end of our Sun in 5 billion years Fate of high mass stars RED SUPER GIANT After Helium exhausted, core collapses again until it becomes hot enough to fuse Carbon into Magnesium or Oxygen. C + C --> Mg OR C + H --> O Through a combination of processes, successively heavier elements are formed and burned. Periodic Table Light Elements Heavy Elements 28Si +4 12 416 1 12 16 12 16 12 4He 20 24 32 16 He He 7( 3( 4 CO4(4+ He) + He) +H) C-N-O C O C O 56 Ni C Cycle Ne Mg S O ++ +energy energy +++energy energy energy energy 56Fe The End of the Line for Massive Stars Massive stars burn a succession of elements. Iron is the most stable element and cannot be fused further. Instead of releasing energy, it uses energy. Supernova ! BEFORE AFTER Supernova Remnants: SN1987A a b c d a) Optical - Feb 2000 • Illuminating material ejected from the star thousands of years before the SN b) Radio - Sep 1999 c) X-ray - Oct 1999 d) X-ray - Jan 2000 • The shock wave from the SN heating the gas Supernova Remnants: Cas A Optical X-ray Elements from Supernovae All X-ray Energies Calcium Silicon Iron What’s Left After the Supernova Neutron Star (If mass of core 4 -10x Sun) • 10 - 20 Km across • Gives off pulses of radiowaves Black Hole (If mass of core > 10x Sun) • So dense light cannot escape! • Gives off x-rays Black Holes - Up Close and Personal Accretion Disk Singularity (deep in center) Event Horizon Jet (not always present) A NEW LIFE BEGINS SHOCK WAVES from a Supernova . Another nebula starts to condense. A PROTOSTAR forms Which Brings us Back to ... blackhole protostar red supergiant nebula SUPERNOVA main sequence pulsar nebula black dwarf protostar main sequence red giant white dwarf