Rieke and his colleagues used Spitzer's infrared eyes to study 266 nearby stars of various ages that were between two and three times the size of the sun. The team discovered that 71 of the stars had planet-forming disks surrounding them. We thought young stars, about one million years old, would have larger, brighter disks, and older stars from 10 to 100 million years old would have fainter ones, Rieke explains. That's because astronomers believed that as the planetoids got bigger, fewer collisions took place within the disks. But we found some young stars missing discs and some old stars with massive disks, he says.
The findings suggest planet formation can take up to 10 times longer than previously thought. Rieke notes that huge collisions are necessary to produce the amount of dust seen in the new images and to replenish the material in the disks over the longer time frame. The study results will appear in an upcoming issue of the Astrophysical Journal.