My Crossword Puzzle

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Across
  1. 3. Older galaxies that are the second most common type of galaxy
  2. 7. A system of planets and dwarf planets gravitationally bound together
  3. 9. The explosion of a star
  4. 11. A large cloud filled with dust and gas in space
  5. 13. The force that attracts everything near it towards the center
  6. 14. A standard unit of measurement
Down
  1. 1. Required to back up a statement
  2. 2. The galaxy that Earth is inside of
  3. 4. The average distance between the Earth and the Sun
  4. 5. All space, time, matter, and energy on Earth
  5. 6. An object so dense that anything within a certain radius cannot leave its gravity
  6. 7. A way to prove any statement right or wrong
  7. 8. Most of the known galaxies are this:
  8. 10. The distance of how far light moves in one year
  9. 12. A collection of stars, dust, and gases held up by gravity