Big History: Crossword puzzle

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Across
  1. 2. Formed by the high temperature from a star's death
  2. 6. Elements exist on earth in very ____ amounts
  3. 9. Valuable resources on earth like ____ and gold can only be formed in the death of stars
  4. 10. These are formed by groups of galaxies
  5. 12. Very large stars can ____ iron
  6. 14. Simply burns out when there's not much in the way of fuel
  7. 15. The larger the atom, the more ____ is required
  8. 16. Result of an explosion from the death of a star
  9. 17. It was relatively cool and uniform before stars existed
  10. 19. Fusion of helium to carbon depends on the ____ of the star
  11. 20. This is a group of stars
Down
  1. 1. Individual hydrogen and helium atoms when brought together by gravity forms ____ ____
  2. 3. A star will ____ when it runs out of fuel
  3. 4. A star will eventually consume all the hydrogen that powers its ___ ___
  4. 5. Plays a role in bringing individual hydrogen and helium atoms together to form gas clouds
  5. 7. It will start to burn helium when hydrogen fuel runs out.
  6. 8. When energy is added to a group of atoms, some of the energy converts into ____ ____
  7. 11. Burns at incredible levels
  8. 13. Can be large and made of gasses,or smaller and rocky
  9. 18. Heavy, high stable, and cannot be fused further