Investigating rocking shadows in protoplanetary disks

Investigating rocking shadows in protoplanetary disks

This is a still from a simulation of a forming planetary disk created by University of Warwick and Stephen Hawking Research Fellow Rebecca Nealon. The images show the rotating inner disk in the upper half and the shadow it casts on the outer disk in the lower half. Credit: Rebecca Nealon/University of Warwick

Astronomers at the University of Warwick are unveiling a new phenomenon called the “rocking shadow” effect, which describes how disks in forming planetary systems align and move around their host star. The effect also provides clues as to how they might evolve over time. dr Rebecca Nealon presented the new work at the 2022 National Astronomy Meeting at the University of Warwick this week.

Stars are formed when a large cloud of gas and dust collapses. The leftover material that doesn’t make it into the star circles around it, much like water swirls around the drain before falling in. This swirling mass of gas and dust is called the protoplanetary disk, and it is here that planets like Earth are born.

Protoplanetary disks are often thought to be shaped like dinner plates – thin, round, and flat. However, recent telescopic images from the Atacama Large Millimeter/submillimeter Array (ALMA) show that this is not always the case. Some of the disks observed by ALMA exhibit shadows, with the part of the disk closest to the star blocking some of the starlight and casting a shadow on the outer part of the disk. From this shadow pattern it can be concluded that the inner part of the disk is oriented completely differently than the outer part, in a so-called broken disk.

Film from the 3D simulation of a disk in a forming planetary system. The inner pane casts shadows on the outer pane, which rocks back and forth. Credit: Rebecca Nealon/University of Warwick

In this research, the team used high-performance computers to run three-dimensional simulations of a shattered pane. The team then created a mock observation, modeling what such a disk would look like when viewed through a telescope and how it would change over time.

As the inner disk moved under the gravitational pull of the central star, the shadow it cast moved across the outer disk. But instead of the shadow pattern moving around the disk like a clock hand, as expected, it rocked back and forth in a seesaw-like motion. Although the inner disc always rotated in the same direction, its shadow looked like it was rocking back and forth. The team suspects that this is caused by a geometric projection effect that is likely to occur with all broken panes.

Nealon says that “JWST promises to give us a look at embryonic planetary systems in unprecedented detail, and with our new models we will be able to learn much more about planet birth.”

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Provided by the Royal Astronomical Society

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