How do we learn about what is going on in the center of our own ...

[karen]

How do we learn about what is going on in the center of our own galaxy (the Milky Way)?
 
  A) We have learned it only recently, thanks to the great photographs obtained by the Hubble Space Telescope.
  B) We cannot see the galactic center with visible or ultraviolet light, but radio and X-rays from the center can be detected.
  C) The gas and dust in the Milky Way prevent any type of direct observation of the galactic center, but theoretical models allow us to predict what is happening there.
  D) We must look at the centers of other galaxies and hope that ours is just like others.
  E) We can study it with visible telescopes as with any other star in the Galaxy.

Question 2

What fraction of the mass needed to halt expansion is known to exist in the form of visible mass in the universe?
 
  A) 1 percent
  B) 4 percent
  C) 22 percent
  D) 74 percent
  E) 100 percent

[Yixagurpuldink]

Answer to Question 1

B

Answer to Question 2

A

[karen]

Thanks for the timely response, appreciate it

[sultansheikh]

Gracias!