Chapter three crossword puzzle

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Across
  1. 6. the prevailing model of how the universe was created
  2. 8. Gravity forced ______ nuclei in their cores to fuse
  3. 12. much smaller than planets
  4. 14. when the cores of the stars collapsed, the outer layers also zoomed
  5. 15. the stars cores imploded, collapsing thousands of miles in just seconds from about the size of the Earth to about ______ mile in diameter
  6. 16. so dense that a single teaspoon of its material on Earth would weigh 1 billion tons
  7. 18. first scientist to argue that neutron stars might create heavy elements such as gold
  8. 19. a mixture of two or more metals
  9. 20. Proton has what kind of charge
Down
  1. 1. the unnamed stars thrived on
  2. 2. important pair of large stars formed and started circling each other
  3. 3. Neutron has what kind of charge
  4. 4. humans never laid eyes on the gold in
  5. 5. space rock that hit a planet's surface
  6. 7. soft, highly conductive, and doesn't corrode, making it suitable for use in electronics
  7. 9. the unit to express the percentage of pure gold in an alloy
  8. 10. pulls atoms closer together into swirling clumps of gas and dust
  9. 11. Karats misspelled
  10. 13. a science writer from Cleveland, Tenn
  11. 17. How many stars involved in the creation of gold thrived on nuclear fusion