This explains it

I thought it was just dog hair and dust causing those tumbleweeds in the corners of my room. But obviously, it's just the formation of a new solar system.

"The dust bunnies under your bed grow in a similar way," said Scott Kenyon, a planet-formation theorist at the Harvard-Smithsonian Center for Astrophysics. "And after a million years, a dust bunny can get pretty big."