A group of global astronomers spearheaded by Richard Teague, the Kerr-McGee Career Development Professor in the Department of Earth, Atmospheric, and Planetary Sciences (EAPS), has compiled the most exquisite and thorough observations of 15 protoplanetary disks to date, providing the astronomical community with fresh insights on the processes of initial planetary development.
“The innovative techniques we’ve created to collect this data and imagery are akin to transitioning from reading glasses to high-powered binoculars — they unveil an entirely new level of detail in these systems where planets form,” remarks Teague.
Their open-access results were published in a special compilation of 17 articles in the Astrophysical Journal of Letters, with additional publications anticipated this summer. The report illuminates a wide range of inquiries, including methodologies to determine the mass of a disk by gauging its gravitational impact and deriving rotational velocity profiles with a precision of meters per second.
Protoplanetary disks are aggregates of dust and gas surrounding nascent stars, from which planets emerge. Observing the dust in these disks is simpler because it is more luminous; however, the insights gleaned from dust alone provide only glimpses of the underlying activities. Teague’s research has pivoted towards examining the gas in these systems, as it can offer deeper understanding of the dynamics within a disk, including characteristics such as gravity, velocity, and mass.
To attain the required resolution for gas study, the exoALMA program invested five years coordinating extended observation periods at the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. Consequently, the international cohort of astronomers, many being early-career researchers, managed to capture some of the most intricate images ever recorded of protoplanetary disks.
“The remarkable aspect of the data is its quality; the community is devising new tools to extract signatures from planets,” states Marcelo Barraza-Alfaro, a postdoc in the Planet Formation Lab and a participant in the exoALMA project. Several innovative techniques were established to enhance and calibrate the captured images, thereby maximizing the heightened resolution and sensitivity achieved.
As a result, “we are discovering new phenomena that compel us to adjust our comprehension of what’s occurring in protoplanetary disks,” he asserts.
One of the papers with significant influence from EAPS examines planetary formation via vortices. For some time, it has been established that the straightforward model of formation frequently suggested, where dust grains coalesce and “snowball” into a planetary core, is insufficient. One potential assistance may come from vortices, or localized disturbances within the gas that draw dust toward the center. Here, they are more inclined to cluster, reminiscent of soap bubbles gathering in a draining bath.
“We can observe the accumulation of dust in various regions, but we cannot determine its movement,” remarks Lisa Wölfer, another postdoc in the Planet Formation Lab at MIT and the lead author of the paper. While astronomers can confirm that the dust has congregated, insufficient information prevents them from concluding how it reached that state.
“Only through the dynamics of the gas can we definitively verify that it’s a vortex and not another phenomenon, creating the structure,” she notes.
During the data collection phase, Teague, Wölfer, and Barraza-Alfaro developed simplified models of protoplanetary disks for comparison with their observations. However, upon receiving the data, their models failed to account for what they observed.
“Upon reviewing the data, we found none of our previous models were viable. It was significantly more intricate,” explains Teague. “Earlier, there was a common belief that they were static. That’s far from the truth.”
The team was compelled to reassess their models and utilize more complex ones that incorporate greater gas motion, which require additional time and resources to execute. Nevertheless, initial findings are encouraging.
“We observe that the patterns are remarkably alike; we consider this the optimal test case for further study with additional observations,” states Wölfer.
The new data, now publicly available, arrives at a propitious moment: ALMA will be undergoing a period of inactivity in the coming years while it is upgraded. During this interval, astronomers can persist with the monumental task of analyzing the collected data.
“It will continuously yield results for many years ahead,” concludes Teague.