Astronomers Chase A Game Of Shadows Around A Planet-Forming Star

Observations of HD135344B in May 2016. Tomas Stolker (University of Amsterdam)/ESO

An international team of astronomers has observed and followed shadows in the outer disk that surrounds a young star and they are using these features to better understand the workings of the inner disk, which they think is casting the shadows but can’t be imaged directly yet.

The study, accepted for publication in the Astrophysical Journal, looked at star HD135344B, which is located 350 light-years from Earth. The system has caught the astronomers' attention because it sports striking spiral features likely caused by forming gas giant planets, like Jupiter.

In 2015, observations were performed to better characterize the system and astronomers spotted this shadow. The following year, to get a better understanding, the team used the SPHERE instrument, which is part of the Very Large Telescope in Chile, to take repeated observations over a two-month period to try and get more solid evidence that the inner disk is to blame for these shadows.

“It may be winds, or swirls or clashes of pebbles,” lead author Dr Tomas Stolker, currently at ETH in Zurich but at the time at the University of Amsterdam, said in a statement.

“Two years ago, we already expected that the shadows on the outer disk were caused by processes in the internal disk. Unfortunately, we cannot see that part of the disk directly with SPHERE. But due to additional observations with SPHERE, we observed the shadows on the outer disk better, and therefore we now know more about the inner disk.”

This is not the first shadow spotted in a protoplanetary disk. At the beginning of the year, something similar was observed happening around TW Hydrae. In that case, researchers believed that a massive planet was causing the internal disk to be twisted.

It is too early to say what’s causing the shadow, but finding more example of these type of systems suggests that they might be very common. The team is hoping to perform another round of observations on HD135344B, ideally with images taken just a few days apart.

Future observatories, like the James Webb Space Telescope, might do even better. Looking further into the internal disk, they might be able to catch the shadow-caster directly, or at least perform observations that can help exclude certain scenarios. 

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