"The yearly ritual of spring cleaning clears a house of dust as well as dust 'bunnies', those pesky dust balls that frolic under beds and behind furniture. NASA/ESA Hubble Space Telescope has photographed similar dense knots of dust and gas in our Milky Way Galaxy. ..."
Follow the link for a more complete explanation. And while you are there, try browsing around www.spacetelescope.org for more interesting images.