The Universe

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Across
  1. 4. galaxies with rotating arms extending from a central bulge
  2. 5. curved regions of stars and gas extending outward in a spiral galaxy
  3. 8. two small irregular galaxies near the Milky Way
  4. 10. galaxy the spiral galaxy that contains our solar system
  5. 12. the dense central region of a galaxy filled with older stars
  6. 15. a star that changes brightness as it expands and contracts
  7. 17. the central region of a galaxy where stars are densely packed
  8. 18. the time it takes the Sun to orbit the center of the Milky Way once
  9. 19. invisible matter believed to make up most of the universe’s mass
Down
  1. 1. the spherical outer region of a galaxy containing old stars and globular clusters
  2. 2. stars younger stars rich in heavy elements found mainly in spiral arms
  3. 3. rounded galaxies with little gas or dust and few young stars
  4. 6. stars older stars with fewer heavy elements found in halos and bulges
  5. 7. the cluster of galaxies that includes the Milky Way and nearby galaxies
  6. 9. the flat rotating region of a galaxy containing most of its stars and gas
  7. 11. stars that suddenly brighten because of violent activity or explosions
  8. 13. stars whose brightness changes over time
  9. 14. galaxies without a definite shape or structure
  10. 16. a large collection of stars, gas, dust, and other objects held together by gravity