Little “hurricanes” can be used to study certain aspects of planetary formation

Planet formation in protoplanetary disks begins through core accretion, where gravity causes particles in the disk to stick together. The process eventually leads to the formation of large solid bodies such as asteroids or planets. After a planet is born, it begins to carve indentations into the protoplanetary disc, like grooves on a vinyl record.

In addition to the grooves, ALMA observations have revealed additional exotic structures in protoplanetary disks, including clusters and arcs with shapes resembling bananas or peanuts. It was assumed that the planets are also responsible for the operation of at least some of these structures.

There must be something causing these structures to form. One possible mechanism for producing these structures – and certainly the most interesting one – is the dust particles that we see as arcs and clumps concentrated in the centers of fluid vortices: essentially tiny cyclones that can occur due to certain instabilities in the edges of the cavities carved in protoplanetary disks by planets.

Researchers from the University of Cambridge and the Institute for Advanced Study have developed a method that uses observations of these “hurricanes” by the Atacama Large Millimeter/Submillimeter Array (ALMA) to put some constraints on the mass and age of planets in the young star. the system. According to the researchers, these small “hurricanes” can be used to study certain aspects of planet formation, even for smaller planets that orbit their star at great distances and out of reach of most telescopes.

The two researchers first theorized how long it would take for a planet to create a vortex in the disk to develop their technology. Then, by placing fewer constraints on the planet’s mass or age, they used these calculations to constrain the parameters of the planets in the vortex disks. They refer to these methods as “vortex dating” and “vortex weighing” of planets.

The tale gap in the disk results from a growing planet that started pushing material from the disk away once it got big enough. As a result, the material on the outer gap increases in density more than the material inside the gap. Instability may occur as the gap widens and the intensity differences increase. This instability leads to disc disruption, which can eventually lead to a vortex.

Ph.D. Student Nicholas Simmerman said, “Over time, multiple vortices can merge and evolve into one large arc-like structure that we observed with ALMA. Because vortices need time to form, the researchers say their method is like a clock that can help determine a planet’s mass and age.”

Lead author Professor Roman Rafikov from the University of Cambridge’s Department of Applied Mathematics and Theoretical Physics said: “More massive planets produce vortices early in their evolution because of their stronger gravity, so we can use vortices to put some constraints on a planet’s mass, even if we can’t see the planet directly.”

Astronomers can estimate a star’s age using many data points such as luminosity, velocity, and spectra. With this knowledge, the Cambridge researchers calculated the smallest planet mass that might have been in orbit since the formation of the protoplanetary disk and were able to generate the observable ALMA vortex. This enabled them to estimate the planet’s mass without observing it directly.

Scientists have found that the potential planets responsible for these swirls must have masses of at least tens of Earth masses, in the super-Neptunian range, by applying this technique to several known protoplanetary disks with significant arcs suggestive of swirls.

Cimerman said, “I often focus on the technical aspects of performing simulations in my day-to-day work. It’s exciting when things come together, and we can use our theoretical results to learn about real systems.”

Rafikov said, “Our limitations can be combined with those provided by other methods to improve our understanding of the properties of planets and the pathways of planet formation in these systems. By studying planet formation in other star systems, we may learn more about how our solar system evolved.”

Journal references:

  1. Roman R. Rafikov and Nicholas Simmerman. “Vortex Weighting and Dating of Planets in Protoplanetary Disks.” Monthly Notices of the Royal Astronomical Society (2022). DOI: 10.1093/mnras/stac3692 or DOI: 10.48550/arXiv.2301.01789
  2. Nicola B. Simmerman and Roman R. Rafikov. Swirls appear at the edges of planet-driven recesses in protoplanetary disks. Monthly Notices of the Royal Astronomical Society (2022). DOI: 10.1093/mnras/stac3507

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