How does the density wave theory explain the presence of young ...

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How does the density wave theory explain the presence of young stars in the spiral arms?
 
  What will be an ideal response?

Question 2

Ionization from the ___________________ _ star in the Orion nebula makes it ___________________ _ brightly.
 
  Fill in the blank(s) with correct word

[Moriaki]

Answer to Question 1

Spiral arms are dynamically stable regions of compression that move slowly around the galaxy. Gas clouds moving at orbital velocity around the galaxy overtake the slow-moving arms from behind and slam into the gas already in the arms. The sudden compression of the gas can trigger the collapse of the gas clouds and the formation of new stars. Newly formed stars and the remaining gas eventually move on through the arm and emerge from the front of the slow-moving arm to resume their travels around the galaxy.

Answer to Question 2

hottest; glow

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Thanks

[Moriaki]

Welcome