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Galaxies and stars


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Galaxies and stars

  1. 1. The Universe……is space and everything in it.
  2. 2. GalaxiesA galaxy is a cluster of stars, gas, and dust that are held together by gravity. Thereare three main types of galaxies:  Irregular  Elliptical  Spiral
  3. 3. Types of Galaxies – Irregular… Some galaxies do not have definable, regular shapes and are known as irregular galaxies. They contain young stars, dust, and gas.
  4. 4. Types of Galaxies – Elliptical...Ellipticalgalaxies look like flattened balls.These galaxies contain billions of stars, but have little gas and dust between the stars.Because of the lack of gas anddust, new stars cannot form inmost elliptical galaxies, and so theycontain only old stars.
  5. 5. Types of Galaxies –Spiral…Spiral galaxies consist of aflat, rotating disk with stars, gas,and dust and a centralconcentration of stars, knownas the bulge. The bulge issurrounded by a much fainterhalo of stars.Contains middle aged stars
  6. 6. Types of Galaxies – Barred Spiral…Our Milky Way galaxy hasrecently (in the 1990s) beenconfirmed to be a type ofspiral galaxy known as abarred spiral galaxy.Our Sun is located at theedge of the Milky Waygalaxy.
  7. 7. Nebulae (plural for Nebula) Stellar Nebula- A gigantic cloud of gas and dust from which stars are made; sometimes called a “Stellar Nursery” Planetary Nebula- When a star runs out of fuel to burn, its outer layers of gas are blown outward in the shape of a ring.
  8. 8. StarsA star contains hydrogen gas that forms helium through a process known as nuclear fusion. Stars form when gravity pulls together gas and dust from stellar nebula. Itreleases enormous amounts of energy which causes the star to become very hot and glow. Vary in mass, size, and temperature Held together by gravity.
  9. 9. A Star is Born…A star is made up of a large amount of gas, in a relatively small volume.A stellar nebula, on the other hand, is a large amount of gas and dust, spread out in an immense volume. All stars begin their lives as parts of stellar nebulas.
  10. 10. A Star is Born… Gravitycan pull some of the gas and dust in a nebula together. The contracting cloud is then called a protostar.A star is born when the contracting gas and dust become so hot that nuclear fusion begins.
  11. 11. Lifetimes of Stars… Beforethey can tell how old a star is, astronomers must determine its mass. Medium mass stars, such as the Sun, exist for about 10 billion years. These are known as main sequence stars.
  12. 12. Lifetimes of Stars… Starswith more mass have shorter lives than those with less mass. Small stars use up their fuel more slowly than large stars, so they have much longer lives, about 200 billion years.
  13. 13. Lifetimes of Stars…Stars form in a stellarnebula, from collapsingclouds of interstellar gasand dust. This is called aprotostar. The rest of the life cycle depends on the mass of theWhen a star runs out of star.fuel, it will become a whitedwarf, neutron star, orblack hole.
  14. 14. Main Sequence Stars… Main Sequence is the stage in which stars spend the majority of their lifetime. Small and medium stars first become red giants. Theirouter layers expand during the red giant phase. Eventually, the outer parts grow bigger still and drift out into space.
  15. 15. Main Sequence Stars... Theblue, white, hot core is left behind causing a white dwarf. When there is no more energy, it becomes a black dwarf. It is the remaining burnt-out cinder left, as the star goes out.
  16. 16. A dying giant, or supergiant star, can suddenly explode. Within hours, the star blazes millions of times brighter. The explosion is called a supernova.
  17. 17. Neutron Stars… After a star explodes, some material from the star is left behind. This material may become part of a planetary nebula. Thecore will compress and form a neutron star. Neutron stars are even smaller and more densethan white dwarfs.
  18. 18. Black Holes… Themost massive stars may have more than 40 times the mass of the Sun. One might have more than five times the mass of the Sun left, after it becomes a supernova. The gravity of this mass is so strong that the gas is pulled inward, packing it into a smaller and smaller space. These massive stars become black holes when they die.