"Grease" was chosen by the science writers, astronomers call this stuff PAHs just like a chemist would. It condenses into "dust grains", so no, it's not only a

"Grease" was chosen by the science writers, astronomers call this stuff PAHs just like a chemist would. It condenses into "dust grains", so no, it's not only a gas. These reason you can't see much in the plane of our galaxy is that these dust grains block visible light.