Pebble density increases with time. The black regions have no pebbles, blue regions have a moderate density, and bright regions have high density of pebbles. The square represents a small part of the disk of gas and dust that surrounds the star before the planets form, referred to as the protoplanetary disk, seen from above.
Some stars are lonely behemoths, with no surrounding planets or asteroids, while others sport a skirt of attendant planetary bodies. New research published this week in The Astrophysical Journal Letters explains why the composition of the stars often indicates whether their light shines into deep space, or whether a small fraction shines onto orbiting planets.