science crossword puzzle

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Across
  1. 3. what are planets pulled to by gravity?
  2. 8. what is one thing that makes a nebula?
  3. 9. when gravity's greatest mass was at center?
  4. 10. what is surrounded by gasses?
  5. 12. one of the first elements created is?
Down
  1. 1. what releases radiation?
  2. 2. e=mc2 is a theory created by who?
  3. 4. what are the building blocks of matter?
  4. 5. when galaxies move away from each other
  5. 6. what orbit around the sun?
  6. 7. what happens when nuclear fusion begins?
  7. 11. everything came from one point of what?