What is the dark rift?

I understand that it's theorized to be dark clouds that creates this band of seemingly empty space in our milky way(and other galaxies as well).

How do we know it's clouds, and not actually just empty space?

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Because background stars are actually shining through in the infrared.

 

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Besides the infrared suns, is there any other evidence supporting this cloud theory?

 

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Just as a starter,

1. In addition to the infrared, can see through the Great Rift in radio, gamma, and x-ray frequencies.

2. Telescopes focused on regions of the Great Rift show star forming regions and things that look at lot like clouds.

3. We see the exact same feature in other galaxies. http://www.google.com/images?q=edge-on galaxy

 

thank you for the link. It's very pretty