PI: Ken Rice

The goal of this project was to understand the evolution of solids in gravitationally unstable protostellar discs. It’s becoming increasingly clear that planet formation starts during the earliest stages of star formation when these discs are also susceptible to the gravitational instability. Therefore, it seems likely that this phase may play a role in the growth of planet building material.

In this project, we used shearing boxes to evolve gravitationally unstable protostellar discs at high resolution. The simulations also included solid particles that ranged in size from about 1mm to 100cm. The gravitational instability manifests as spiral density waves in the gas disc that can enhance the local density of solids, in particular particles with sizes of around 10cm.

As shown in Figure 1, if the solid particle size distribution extends beyond about 10cm and if the dust-to-gas ratio was about 0.01, then the enhancement of the solids in the spirals could lead to the direct gravitational collapse of the solid component in these discs. The objects that form tend to have masses between 0.1 Earth masses and 10 Earth masses. Given that a dust-to-gas ratio of 0.01 is what is expected in these discs, this presents a viable mechanism for forming the key building blocks of planets.

Figure 1: Surface density of solids in discs with dust-to-gas ratios ranging from 0.0001 (top-left panel) to 0.025 (bottom-right panel). The bottom two panels show the formation of dense clumps that have masses between 0.1 Earth masses and 10 Earth masses.