Shadow oscillation in protoplanetary disks

July 15 () –

Astronomers describe a new phenomenon – the ‘oscillating shadow’ effect – that describes how disks in forming planetary systems are oriented and how they orbit their host star.

Stars are born when a large cloud of gas and dust collapses in on itself. The extra material that doesn’t make it to the star ends up swirling around it, similar to how water swirls around a drain before it falls. This swirling mass of gas and dust is called a protoplanetary disk, and it is where planets like Earth are born.

Protoplanetary disks are often thought to be shaped like dinner plates: thin, round, and flat. However, recent images from the Atacama Large Millimeter/Submillimeter Array (ALMA) show that this is not always the case. Some of the disks seen by ALMA have shadows, where the part of the disk closest to the star blocks some of the starlight and casts a shadow on the outer part of the disk. From this pattern of shadows, it can be inferred that the inner part of the disk is oriented completely differently than the outer part, in what is called a broken record.

In this investigation, presented at the National Astronomy Meeting, the University of Warwick team used high-performance computers to run three-dimensional simulations of a broken disk. The team then produced a simulated observation, modeling what such a disk would look like if viewed through a telescope. and how it would change over time.

As the inner disk moved through 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, reports the University of Warwick in a statement.

So even though the inner disc was still spinning in the same direction, its shadow seemed to sway back and forth. The team suggests this is due to a geometric projection effect, which is likely to happen on all broken disks.