physics puzzle

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Across
  1. 2. positive charge
  2. 3. cloud of dust
  3. 4. creation of the universe
  4. 6. explosion of a star
  5. 8. same atomic number but different atomic mass
  6. 9. a single dense point
Down
  1. 1. negative charge
  2. 2. ionized gas
  3. 5. neutral charge
  4. 7. biggest evidence of the big bang