This award will support a theoretical effort to explore the effects of turbulence in accretion disks around very young stars. The modern understanding of disk theory requires the presence of turbulence in order to provide the viscosity necessary for angular momentum transport. Turbulence can also assist the trapping of solids needed to quickly aggregate dust into progressively larger bodies, leading to planet formation. The theoretical models to be used are based on three-dimensional magnetohydrodynamical calculations, and include the effects of resistivity and gas cooling.
The research is expected to improve the understanding of accretion onto stars and the environment in which planet formation occurs. The research team plans to create computer visualizations based on the simulations used for this project, and to distribute these to the astronomical community. They will also participate in ongoing outreach and public education efforts at the American Museum of Natural History.
This award supported investigation of the structure and motions of disks of partly charged gas and dust around young stars as planets form in them. This investigation was performed using supercomputer simulations and mathematical analysis, based on our knowledge of the physics of the dilute, partly magnetized, dusty gas that forms these disks. Analogous motions were also studied in the similar disks that form around the massive black holes found in the centers of galaxies. Major results of the award include the following: 1. Large vortexes can form in disks in the boundaries between regions where the charge of the plasma is high enough to support magnetically-driven turbulence and regions where the gas flows smoothly. These vortexes can concentrate the dust enough to form the building blocks of planets 2. Planets interact by gravity with the gas of the disk, which cause them to move inwards or outwards. These motions once were thought to lead them to fall into their host star, but instead they accumulate at radii determined by the temperature structure of the disk. Similar results hold for stars in disks around massive black holes in the centers of galaxies. 3. Magnetized turbulence in disks produces hot spots that can reach high enough temperatures to melt rocks. These may explain the nature of the minerals found in the oldest rocks in the Solar System, chondritic meteorites. 4. The interaction of the dust with the gas at late times when most of the gas has already been removed from the system can produce sharp rings comparable to structures that have been observed. This calls into question the usual interpretation of these structures as being caused by yet unobserved planets. This project contributed to the training of three postdoctoral fellows, two PhD students, and four undergraduate students. Contributions to three major, open source, magnetized gas dynamics simulation packages were made. During work on this project, the PI, Mac Low, helped found, and taught the astronomy & space science class in, a residency-based MA in Teaching Earth Science at the American Museum of Natural History where he is a curator. This project relied heavily on his professional understanding of earth and planetary science, built up in part during the research reported on here. The third cohort of 16 students is currently enrolled, and over 35 teachers have already graduated. Unusually, all of the first cohort of teachers have remained in the profession beyond their first year, a stark comparison to the usual drop out rates of as high as 50%.
