Why is it surprising that spiral arms are stable structures, ...

[codyclark]

Why is it surprising that spiral arms are stable structures, lasting billions of years?
 
  a. Differential rotation should tear the arms apart.
 b. Gas and dust clouds should run out of material to make young stars.
  c. Supernova explosions should disrupt the arms.
 d. Globular clusters are continuously passing through the arms.
 e. Gravity should pull the arms down into the center of the galaxy.

Question 2

According to the theory of general relativity, gravity is caused by the ____.
 
  a. linear motion of stars
 b. change in mass of a moving body
  c. curvature of space-time
 d. constant speed of light
 e. inertia of a moving body

[jaymee143]

Answer to Question 1

a

Answer to Question 2

c

[codyclark]

Thanks for the timely response, appreciate it

[flexer1n1]

TYSM