Astronomers use ‘little hurricanes’ to weigh and date planets

(ORDO NEWS) — The small “hurricanes” that form in the disks of gas and dust around young stars could help study certain aspects of planet formation.

Researchers at the University of Cambridge have developed a technique that uses observations of these “hurricanes” to establish some limits on the mass and age of planets in a young star system.

The protoplanetary disks surrounding young stars are where the process of planet formation begins.

Thanks to such a phenomenon as core accretion, gravity causes particles in the disk to stick to each other and form larger solid bodies – asteroids and planets. As young planets form, they begin to cut gaps in the protoplanetary disk.

Even a relatively small planet could be capable of creating them. Because small planets can orbit at great distances from their star, traditional exoplanet detection methods cannot be used.

The scientists also found other distinct structures in protoplanetary disks – arcs and banana-shaped clusters. It was believed that some of these structures were also driven by the planets.

“Something must be causing these structures to form,” said lead author of the study, Professor Roman Rafikov.

“One of the possible mechanisms for creating these structures – and by far the most intriguing – is that the dust particles that we see in the form of arcs and clumps are concentrated in the centers of eddies, in fact, small hurricanes that can be caused by a special instability at the edges of ruptures carved into protoplanetary disks by the planet.”

The researchers used this interpretation to develop a method to limit the mass or age of the planet. First, they calculated the length of time it would take to create a vortex in the disk.

They then used these calculations to limit the properties of planets in vortex disks, basically putting lower limits on a planet’s mass or age. They call these methods “vortex weighing” and “vortex dating” of the planets.

When a growing planet becomes massive enough, it begins to push material out of the disk, creating a gap. When this happens, the material outside the gap becomes denser than the material inside the gap. As the gap deepens and differences in density increase, instability can occur.

This instability perturbs the disk and can eventually lead to the formation of a vortex. Over time, several vortices can merge together, turning into one large structure that looks like an arc.

“More massive planets create vortices early in their development due to their stronger gravity, so we can use vortices to put some limits on a planet’s mass even if we can’t see the planet directly,” Rafikov said.


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