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The Life Cycles of Stars RVCC Planetarium - Last updated 7/23/03 Twinkle, Twinkle, Little Star ... How I Wonder What You Are ... Stars have • Different colors Which indicate different temperatures • Different sizes • Different masses The bigger it is, the hotter and the faster a star burns its life away. Stellar Evolution Stars begin their lives as clouds of gas and dust called Nebulas Clouds Contain: •70% H •28% He •2% Heavier Elements Stars start from Nebula Clouds Collapse to Protostar • Nebula compresses • Gravitational pull attracts more material. • Temperature and pressure increases • Nebula shrinks and begins to spin • Spinning nebula begins to flatten into a disk ….A protostar is formed Protostars are forming in Orion Protostars are forming in the Orion Nebula •Pressure builds inside the protostar over millions of years creating heat •Temp increases to 10 million°C •Nuclear fusion begins….A star is born!! •Main Sequence stage of a star begins •It is the longest stage in life of a star Nuclear Fusion ! • At 15 million degrees Celsius in the center of the star, Hydrogen Atoms fuses into Helium. • It takes 4 Hydrogen atoms to make one Helium atom • Sun has 1056 H atoms to burn which would last 8 billions year! The Beginning of the End: Red Giants After Hydrogen is exhausted in core: • Core collapses, releasing energy to the outer layers • Outer layers expand The Core of a Red Giant •Giants are 10 times bigger than the sun •Supergiants are 100 times bigger than the sun Expansion of the outer Layers Betelgeuse – A Red Giant Star Outer Layers are Expelled … … And a Planetary Nebula forms After Helium exhausted, outer layers of star expelled Planetary Nebulae Some Planetary Nebulae are Round As the dead core of the star cools, the nebula continues to expand, and dissipates into the surroundings. … and Bipolar Some look like an Hourglass … .. or a Cat’s Eye … … or even look like an Eskimo! White Dwarfs At Center of a Planetary Nebula … … sits a White Dwarfs White dwarfs shine for billions of years before they cool completely. The Hubble Space Telescope has detected white dwarf stars (circled) in globular clusters: White Dwarfs are Small and Heavy Size of the Earth with the Mass of the Sun “A ton per teaspoon” Nova is a white dwarf star that suddenly increases in brightness by several magnitudes. It fades very slowly. Fate of High Mass Stars • After Helium is exhausted, core collapses again until it becomes hot enough to fuse Carbon into Magnesium or Oxygen. • Through a combination of processes, successively heavier elements are formed and burned. 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. A Massive Star Explodes A Supernova is an exploding massive star Supernova 1987a What’s Left After the Supernova Neutron Star (If mass of core < 5) • Under collapse, protons and electrons combine to form neutrons. Black Hole (If mass of core > 5) • The force of contraction crushes the dense core of the star • The gravity of a black hole is so great that not even light can escape from it. Supernova interaction Supernovae compress gas and dust which lie between the stars. This compression starts the collapse of gas and dust to form new stars. Which brings us back to … Stellar Recycling Supergiant Red Giant Low mass main sequence star Protostar Planetary Nebula High mass main sequence star Nebula Supernova Neutron Star White Dwarf Nova Black Hole Sun-like Stars Massive Stars