New York, Dec 12 (IANS): An entire family of Pluto-size objects may be swarming around the star known as HD 107146, an adolescent version of our own Sun, says a study.

By making detailed observations of the protoplanetary disk surrounding the star, the astronomers detected an unexpected increase in the concentration of dust grains in the disk's outer reaches.

This surprising increase, which begins remarkably far - about 13 billion kms - from the host star, may be the result of Pluto-size objects stirring up the region, causing smaller objects to collide and blast themselves apart.

Dust in debris disks typically comes from material left over from the formation of planets.

"The dust in HD 107146 reveals this very interesting feature - it gets thicker in the very distant outer reaches of the star's disk," said study lead author Luca Ricci, astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

The surprising aspect is that this is the opposite of what astronomers see in younger primordial disks where the dust is denser near the star.

"It is possible that we caught this particular debris disk at a stage in which Pluto-size planetesimals are forming right now in the outer disk while other Pluto-size bodies have already formed closer to the star," Ricci added.

According to current computer models, the observation that the density of dust is higher in the outer regions of the disk can only be explained by the presence of recently formed Pluto-size bodies.

The star HD 107146 is located approximately 90 light-years from Earth and is approximately 100 million years old.

The study appeared in the Astrophysical Journal.