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  1. 1. Scientists believethat our galaxy is abarred spiral galaxy A barred spiral galaxy is a rotating, flat disk of stars, gas and dust with a bar-shaped center made of stars.
  2. 2. A STAR IS BORN Protostar Every star starts out in a mass of clouds and gas called a nebula. causes hydrogen gas in the nebula to spin. As the hydrogen gas spins, it becomes hotter. It begins to glow.
  3. 3. Medium and larger protostars spin until they reach extremely hot temperatures.Through the process of nuclear fusion, hydrogenin the stars begins to turn into helium.This is the same process that goes on in theSun, and makes it able to give light andheat to Earth.
  4. 4. STAR COLORS A star’s color comes from its surface temperature. How does one star come to have a hotter surface temperature than another? It’s a matter of size. The more mass a star has, the hotter the surface temperature.
  5. 5. STARS ARE CLASSIFIED BY THEIR SURFACETEMPERATURE. that is associated to specific spectral patterns the spectral classification includes 7 main types: O, B, A, F, G, K, M. A popular mnemonic for remembering this order is "Oh, Be A Fine Girl, Kiss Me".
  6. 6. MORGAN-KEENAN SPECTRAL CLASSIFICATIONClass Temperature Star Color O 30,000 - 60,000 °K Blue B 10,000 - 30,000 °K Blue A 7,500 - 10,000 °K White F 6,000 - 7,500 °K White (yellowish) G 5,000 - 6,000 °K Yellow (like the Sun) K 3,500 - 5,000 °K Orange M 2,000 - 3,500 °K Red
  7. 7. WHAT IS A NOVA? . A nova is an explosion that happens on a white dwarf, which is a very old star.
  8. 8. This swirl of colorsis made of materialleft from Kepler’sSupernova locatedin the Milky WayGalaxyKepler’sSupernova wasthe lastsupernova seenin our galaxy.
  9. 9. A SUPERNOVA GETS AT THE CORE A supernova is like a nova, except the explosion takes place at the core of the star, not the surface. Every supernova and nova is important, because each explosion creates dust This dust forms the building blocks for nebulae, where new stars are born.
  10. 10. BLACK HOLES After a supernova, a star may leave behind a burned part This part can collapse and absorb the light around it. This is a black hole, the end of a giant star. A star must be 10 to 15 times larger than the Sun in order to end as a black hole. A smaller star will simply cool rather than collapsing.
  11. 11. CLUSTERS OF STARS Open clusters have mostly young, bright, blue stars that were born together.They usually have irregular shapes.At 400 light years away, the Pleiades is Earth’sclosest open cluster. Example is Pleiades
  12. 12. GLOBULAR  can have as many as aCLUSTERS million stars – more than open clusters.  have a sphere-like shape, with many stars at the center.  A globular cluster named M15 is the closest of its kind to Earth.
  13. 13. TYPES OF STARS Protostar a collection of gas that has collapsed down from a giant molecular cloud. Over time, gravity and pressure increase, forcing the protostar to collapse down. All of the energy release by the protostar comes only from the heating caused by the gravitational energy – nuclear fusion reactions haven’t started yet.
  14. 14. T TAURI STAR stage in a star’s formation and evolution right before it becomes a main sequence star. T Tauri stars don’t have enough pressure and temperature at their cores to generate nuclear fusion they do resemble main sequence stars Stars will remain in the T Tauri stage for about 100 million years.
  15. 15. MAIN SEQUENCE STAR Our Sun is a main sequence star, and so are our nearest neighbors, Sirius and Alpha Centauri A converting hydrogen into helium in their cores, releasing a tremendous amount of energy
  16. 16. RED GIANT STAR A shell of hydrogen around the core ignites continuing the life of the star, but causes it to increase in size dramatically. star has become a red giant star, and can be 100 times larger than it was in its main sequence phase. The red giant phase of a star’s life will only last a few hundred million years before it runs out of fuel completely and becomes a white dwarf.
  17. 17. WHITE DWARF STAR When a star has completely run out of hydrogen fuel in its core and it lacks the mass to force higher elements into fusion reaction, it becomes a white dwarf star A white dwarf shines because it was a hot star once, but there’s no fusion reactions happening any more
  18. 18. A white dwarf will just cool down until itbecause the background temperature of theUniverse. This process will take hundreds of billions of years, so no white dwarfs have actually cooled down that far yet.
  19. 19. RED DWARF STAR Red dwarf stars are the most common kind of stars in the Universe. Red dwarf stars are able to keep the hydrogen fuel mixing into their core, and so they can conserve their fuel for much longer than other stars. red dwarf stars will burn for up to 10 trillion years.
  20. 20. NEUTRON STARS If a star has between 1.35 and 2.1 times the mass of the Sun, it doesn’t form a white dwarf when it dies. Instead, the star dies in a catastrophic supernova explosion, and the remaining core becomes a neutron star.
  21. 21. SUPERGIANT STARS The largest stars in the Universe are supergiant stars. supergiants are consuming hydrogen fuel at an enormous rate and will consume all the fuel in their cores within just a few million years. Supergiant stars live fast and die young