Astronomy: Milky Way

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Across
  1. 4. The minor spiral arm (or spur) where our Solar System is located, situated between the larger Sagittarius and Perseus arms.
  2. 5. The supermassive black hole at the very center of our galaxy, with a mass equal to 4 million Suns.
  3. 8. The name comes from the galaxy's appearance as a dim, glowing milky band arching across the night sky.
  4. 11. Clouds Two irregular dwarf galaxies (Large and Small) that orbit the Milky Way and are visible from the Southern Hemisphere.
  5. 12. The dense, spherical tightly packed group of stars found in the center of the galactic disk.
  6. 14. The Milky Way is immense; its visible disk is approximately 100,000 light-years across.
  7. 16. A vast, spherical region enveloping the galactic disk, containing old stars, globular clusters, and dark matter.
  8. 17. Invisible matter that makes up about 90% of the Milky Way's mass; we can't see it, but we detect it through its gravitational pull on stars.
Down
  1. 1. Tightly bound spherical collections of very old stars that orbit in the halo of the galaxy, like satellites.
  2. 2. The small cluster of about 54 galaxies that includes the Milky Way, Andromeda, and the Triangulum Galaxy.
  3. 3. Because dust blocks visible light, astronomers map the shape of the Milky Way using radio astronomy to see through the center.
  4. 6. A star composed almost entirely of hydrogen and helium; the Milky Way's halo contains these ancient stars that lack "heavy metals."
  5. 7. The process where a large galaxy (like ours) absorbs smaller dwarf galaxies through gravitational tidal forces.
  6. 9. The flat, rotating plane of the galaxy containing spiral arms, gas, dust, and young stars (like a fried egg's white).
  7. 10. Our nearest major galactic neighbor; it is on a collision course with the Milky Way and will merge with us in about 4.5 billion years.
  8. 13. Also known as a "cosmic year," this is the time it takes for the Sun to complete one full orbit around the Milky Way (approx. 230 million Earth years).
  9. 15. The theoretical boundary around Sagittarius A* beyond which nothing, not even light, can escape.