Almost all of the large galaxies observed so far have central black holes, each billions of times the mass of our sun.

But about half of these cosmic monsters are obscured by dense rings of dust, and astronomers have been uncertain where all this dust comes from and how it's remained intact over time.

According to the new theory, it's possible that newly formed planets and asteroids whirling close to these giant black holes are continually being smashed to smithereens, creating the thick, donut-shaped clouds of debris.

(Related: "Space Smash-Up Turned Planets to Dust.")