The formation of new planets is believed to start with microparticles of cosmic dust that collide and bind together, eventually creating larger dust aggregates. Over time, these aggregates might combine and evolve into planets. The modeling performed by the Tohoku University team suggests that as these dust aggregates grow in size, the probability of them sticking together after a collision decreases. This could impact the formation rate of planetesimals, the kilometer-sized bodies that serve as the building blocks of planets.
To conduct their study, the team utilized numerical simulations of dust aggregate collisions. They focused on equal-mass aggregates varying in size from 10,000 to 140,000 microns (or one to 14 cm). Their approach differed from previous studies by treating each particle within the aggregate individually, instead of considering the aggregate as a single entity. This allowed the team to account for potential deformations during collisions. Their findings were published in The Astrophysical Journal Letters.
"The formation process of kilometer-sized bodies, planetesimals, from cosmic dust, which is the initial stage of planet formation, has been one of the biggest problems in the theory of planet formation," said Hidekazu Tanaka, a co-author of the study and a professor at Tohoku University's Astronomical Institute.
Their findings show that dust clumps, the raw material for planet formation, stop growing beyond a certain size as large clumps find it difficult to stick together. This raises a new challenge to the prevailing theories of planetesimal formation, according to Tanaka.
Historically, attempts to determine the threshold for the sticking/bouncing barrier of dust aggregate collisions have led to varied results. This inconsistency led some researchers to hypothesize that the size of aggregates might be a contributing factor, a theory supported by the current study's results.
However, it remains unclear why the size of the aggregate impacts the likelihood of collisional sticking. Future research may investigate the packing structure of aggregates over time to help shed light on this issue. Additionally, studies examining the contact sites between aggregates, where most of the collisional energy is dissipated, could provide insights into how larger aggregates eventually stick together.
The researchers also believe that the size of the individual particles within an aggregate, and not just the overall radius of the aggregate, may influence the sticking probability.
The team acknowledges that their current study is only the beginning and there is a need for more comprehensive simulations, as well as laboratory experiments, to fine-tune their models.
The Tohoku University team is already looking ahead to their next challenge: investigating the behavior of larger dust clumps. Using supercomputing power, they intend to simulate collisions between larger dust aggregates to better understand the intricacies of planetesimal formation.
"The results of these large-scale numerical simulations will help us answer the question of whether the formation of planetesimals is possible through the adhesion of dust clumps or not," Tanaka concluded.
Research Report:Size Dependence of the Bouncing Barrier in Protoplanetary Dust Growth
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