sun and beyond our solar system

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Across
  1. 6. galaxies that are grouped up
  2. 10. very large stars
  3. 13. stars pulled towards each other by gravity
  4. 14. large groups of stars
  5. 17. Hubble must be retreating from us at greater speeds
  6. 18. the hottest main sequence stars and the brightest
Down
  1. 1. relationships between the absolute magnitude and temperature of stars
  2. 2. that gives off pulsing radio waves
  3. 3. not even light can escape their surface
  4. 4. stars that end in brilliant explosions
  5. 5. a developing star not hot enough to engage in a nuclear fusion
  6. 7. remains of supernova events
  7. 8. universe began as a violent exploration
  8. 9. a unit to express distance
  9. 11. an area of stars
  10. 12. very bright stars
  11. 15. remains of low mass and medium mass stars
  12. 16. sudden brightness of stars