The metallicity of stellar environments determines the formation of exoplanets
A team of astrophysicists conducted research to more fully understand planet formation in low-metallicity stellar environments. According to previous research, the formation of dust particles large enough to form rocky planets requires a gradual growth from micrometer size to planetesimal size. However, the mechanisms associated with this process in low metallicity environments remain poorly understood.
For their research, astrophysicists conducted a global simulation of the evolution of a viscous disk. They took into account the growth of dust grains, evaporation and condensation of chemicals on snow lines. The researchers also studied different levels of metallicity, disk sizes, and the strength of turbulent viscosity.
As a result of the study, it was found that at solar and subsolar metallicity* there is a significant increase in the mass ratio of dust and gas in the middle plane near the snow lines, but this leads to the formation of planetesimals only near the water ice line. At metallicity [Fe/H] = -0.6 (a value of -0.6 indicates that in this case the amount of iron is slightly less than in the Sun), the formation of several Earth-mass planetesimals is possible.
It turns out that under the extreme conditions of protoplanetary disks, larger disks are preferable to small ones for the formation of a large number of planetesimals with a fixed metallicity, since the pebbles can be preserved for a longer time, which leads to more efficient formation of planetesimals.
At lower metallicity, there is less support for the formation of planetesimals in quiescent disks compared to turbulent disks, since pebbles can be supported for longer periods of time. In simulations, it was found that the number of planetesimals formed at subsolar metallicity limits the size of the core, which can only lead to the formation of super-Earths.
«Subsolar metallicity» — a term used to describe a level of metallicity comparable to that of the Sun. The level of metallicity is measured in comparison to the concentration of iron (Fe) in the Sun. If the metallicity value is 0 (zero metallicity), then this means that the amount of metals in the star is the same as in the Sun.