Rapid-Forming Giant Planets Could Disrupt Spiral Protoplanetary Discs

• Simulations of University of Warwick Astrophysicists show that interactions with giant planets can lead to protoplanetary disks that look older than they should
• Massive young disks are expected to have helical structures, but these are rarely observed with telescopes
• Could be explained by the presence of giant planets at the beginning of the disk’s life

According to a new study by astronomers at the University of Warwick, giant planets that evolved early in the life of a star system could solve a mystery why spiral structures are not observed in young protoplanetary disks.

The on November 26, 2020 in the Astrophysical diary letters A part, supported by the Royal Society, provides an explanation for the lack of a spiral structure astronomers expect in protoplanetary disks around young stars, which also suggests scientists may need to reevaluate how quickly planets move in a disk’s life cycle form.

Protoplanetary disks are the birthplaces of planets and house the material that will eventually merge into a series of planets that we see in the universe. When these disks are young, they form spiral structures with all of their dust and material being drawn into tight arms by the massive gravitational effect of the spinning disk. A similar effect occurs at the galactic level, which is why we spiral galaxies like our own, the Milky Way.

Over the course of three to ten million years, material from the disk comes together to form planets, falls on the star it orbits, or is simply dispersed into space by winds coming from the disk. When a disk is young it is self-gravitating and the material it contains forms a spiral structure that it loses when it becomes gravitationally stable. Young planets as they evolve then carve gaps in the disk as they consume and distribute material in their own way, leading to this ‘Ring and gap features that astronomers see most often in protoplanetary disks.

But astronomers have tried to explain observations of young protoplanetary disks that show no signs of spirals, but look like a much older disk with a ring and fissure structure. To provide an explanation, Sahl Rowther and Dr. Farzana Meru from the Department of Physics at Warwick University performed computer simulations of massive planets in young disks to determine what would happen if they interacted.

They found that a giant planet is about three times the size of JupiterMigration from the outer regions of the disk toward its star would cause sufficient perturbation to obliterate the disk‘s spiral structure with results similar to disks observed by astronomers. However, to exist in the spiral stage of the disk, these planets would have to form quickly and early in the disk’s life cycle.

Lead author Sahl Rowther, PhD student in the Physics Department, said, “When disks are young, we expect them to be massive with spiral structures. But we don’t see that in observations.

“Our simulations suggest that a massive planet in one of these young disks can actually cut the time spent in the self-gravitating spiral phase to one that more closely resembles the observations astronomers see. ”

Video showing the comparison of the development of a protoplanetary disk without planets (left) and with an orbiting 3-Jupiter mass planet (right). Photo credit: University of Warwick

The co-author Dr. Farzana Meru from the Department of Physics adds: “If some of these disks astronomers observe were recently self-gravitated, that suggests that they formed a planet when the disk was young. The self-gravitational phase for a protoplanetary disk is much less than half a million years, which means the planet should have formed incredibly quickly.

“Whichever mechanism explains the formation of these planets, it likely means that we need to take into account that planets are forming much faster than originally thought. ”

Their simulations modeled a giant planet in the outer regions of a protoplanetary disk as it migrates inward. This process is expected by astronomers when the torque pushes the planet inward while exchanging angular momentum with the gas in the disk. This also means that the planet is interacting with a large part of the disk and destroying it and is massive enough to open a gap in the gas, resulting in the ring and fissure structure.

Sahl Rowther adds, “This is exciting given the unknowns associated with the bulk of the disks being observed. If solid disks with ring and gap structures are common, this could provide more avenues for explaining disk architectures.

“Our results suggest that given the right conditions and technologies, it may even be possible to spot signs of these huge planets. The next stage of our research will be to determine the conditions to help astronomers try to determine the presence of these planets. ”

Dr. Meru adds: “It‘It is entirely possible that this spiral structure will be obliterated, don‘Don’t be fooled when looking at a CD. It could still be reasonably massive‘It’s just that a huge planet caused it to lose its spirals.

“We have these amazing pictures of protoplanetary disks and what‘The really exciting thing about them is their structure. In recent years telescopes have become very powerful and so have we‘You can see features like gaps and rings. With computer simulations like ours, we can now try to understand whether some of the processes we expect, like planets wandering in young disks, can lead to the kind of images that observers see. This is possible with the combination of powerful telescopes and supercomputers. ”

Reference: “Hiding Signatures of Gravitational Instability in Protoplanetary Disks with Planets” by Sahl Rowther, Farzana Meru, Grant M. Kennedy, Rebecca Nealon and Christophe Pinte, November 26, 2020, Astrophysical diary letters.
DOI: 10.3847 / 2041-8213 / abc704