Astronomers have captured a remarkable image of a young star surrounded by a deep layer of dust — a layer that's thicker on the outside than it is on the inside, suggesting the presence of an entire family of Pluto-like objects.
The system, called HD 107146, is located approximately 90 light-years from Earth. At 100 million years old, it's a relative newcomer to the galaxy — about 2% the age of our sun. The system is still in the midst of consolidating its massive debris field into planetary bodies, but it has progressed beyond the stage where its protoplanetary disc is solely comprised of dust and rock.
Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers from the Harvard-Smithsonian Center for Astrophysics and the National Radio Astronomy Observatory have detected a surprising concentration of millimeter-sized dust grains in the disc's outer reaches. This is surprising because it's incredibly far from the star — about 8 billion miles (13 billion km). The observation has given rise to the hypothesis that these grains are the result of Pluto-sized planetesimals stirring up the region, causing smaller objects to collide and rip themselves apart.
Artist impression: This adolescent star system shows signs that in its outer reaches, swarms of Pluto-size objects are jostling nearby smaller objects, causing them to collide and "kick up" considerable dust. Caption and image credit: CfA/A. Angelich (NRAO/AUI/NSF).
Interestingly, this is exactly what models predicted. During a solar system's adolescence — the time between the initial dusty period and the formation of fully formed planets — the concentration of dust should be much denser in the outermost regions of the disc.
As noted by Harvard-Smithsonian astronomer Luca Ricci in a release:
The dust in HD 107146 reveals this very interesting feature — it gets thicker in the very distant outer reaches of the star's disk. The surprising aspect is that this is the opposite of what we 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.
Simulations show that the high density of dust in the outer regions can only be explained by the presence of recently formed Pluto-sized bodies, whose gravity would disturb smaller planetesimals, resulting in frequent collisions.
As for the dark ring-like feature in the middle, the astronomers say it may be evidence of a gap where a planet is sweeping its orbit clear of dust.
The star will continue to be studied by astronomers as it's shedding light on how systems transition from its early life to the final stage when planets are done forming.
Read the entire study at The Astrophysical Journal: "ALMA observations of the debris disk around the young Solar Analog HD 107146".