Space and time

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Across
  1. 8. Matter is made up of them
  2. 10. A high redshift source of electromagnetic energy
  3. 12. Study of space
  4. 13. Gaseous environment surrounding a planet
  5. 14. Cannot escape from a black hole
  6. 15. Saturn's largest moon
  7. 16. First discovered black hole is ___ X–1
  8. 18. Closest planet to the sun
  9. 19. Unseen matter
  10. 22. Number of planets in our solar system
  11. 23. Weakest of the four fundamental interactions of physics
  12. 24. Nearest large galaxy to the Milky Way
Down
  1. 1. Origin of the universe
  2. 2. Study of moving bodies
  3. 3. Stargazer
  4. 4. BBH stands for ___ black hole
  5. 5. Lightest element in the universe
  6. 6. Small galaxy
  7. 7. Funniest planet name
  8. 9. System of stars
  9. 11. EHT stands for event horizon ___
  10. 17. Milky Way's central black hole
  11. 20. Belonging in outer space
  12. 21. Largest type of black hole