Astronomers from the University of Warwick have revealed a new phenomenon known as the “wobbly shadow” effect, which describes how the disks that form planetary systems are oriented and how they move around their host stars. The effect also provided clues about how they evolved over time. Dr Rebecca Nealon presented the new work this week at the 2022 National Astronomy Conference at the University of Warwick.
Stars are born when a large cloud of gas and dust collapses on its own. The leftover material that doesn’t make it to the star ends up swirling around it, unlike the way water swirls around a drain before falling in. This swirling mass of gas and dust is called a protoplanetary disk, and it’s where planets like Earth were born.
Protoplanetary disks are often thought of as shaped like dinner plates—thin, round, and flat. However, recent telescopic images from the Atacama Large Millimeter/submillimeter Array (ALMA) suggest that this is not always the case. Some of the disks seen by ALMA were shadowed, with the portion of the disk closest to the star blocking some of the star’s light and casting a shadow on the outer part of the disk. From this shadow pattern it can be deduced that the inside of the disc is oriented completely differently from the outside, the so-called broken disc.
In this study, the team used high-performance computers to perform 3D simulations of damaged discs. The team then performed simulated observations of what such a disk would look like if viewed through a telescope, and how it would change over time.
As the inner disk moves by the gravity of the central star, it casts a shadow across the outer disk. But instead of moving around the disc as expected by the hands of the clock, the shadow pattern wobbles back and forth in a seesaw-like motion. So while the disc inside keeps turning in the same direction, its shadow seems to sway back and forth. The team believes this is caused by geometric projection effects, which are likely to occur in all broken disks.
Our research is important because it bridges the gap between theory and observation. Given new observations from telescopes like the JWST, our cutting-edge numerical techniques mean we have multiple tools to interpret the data and learn more about how planets are born.
“JWST promises to allow us to understand embryonic planetary systems in unprecedented detail, and with our new model, we will be able to learn more about planetary birth,” said Rebecca.