Starship Asterisk*

The young star TW Hydrae is playing ‘shadow puppets’ with scientists

This illustration is based on Hubble Space Telescope images of gas and dust discs encircling the young star TW Hydrae. We have an oblique view of three concentric rings of dust and gas. At the centre is the bright white glow of the central star. The reddish-coloured rings are inclined to each other and are therefore casting dark shadows across the outermost ring. Credit: NASA. ESA, L. Hustak (STScI)

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In 2017 astronomers reported discovering a shadow sweeping across the face of a vast pancake-shaped disc of gas and dust surrounding the red dwarf star TW Hydrae. The shadow isn’t from a planet, but from an inner disc slightly inclined relative to the much larger outer disc — causing it to cast a shadow. One explanation is that an unseen planet’s gravity is pulling dust and gas into its inclined orbit.

Now, a second shadow — playing a game of peek-a-boo — has emerged in just a few years between observations stored in Hubble's MAST archive. This could be from yet another disc nestled inside the system. The two discs are likely evidence of a pair of planets under construction.

TW Hydrae is less than 10 million years old and resides about 200 light-years away. In its infancy, some 4.6 billion years ago, our Solar System may have resembled the TW Hydrae system. Because the TW Hydrae system is tilted nearly face-on as seen from Earth, it is an optimum target for getting a bird’s-eye view of a planetary construction yard.

The second shadow was discovered in observations obtained on 6 June 2021, as part of a multi-year programme designed to track the shadows in circumstellar discs. John Debes ... compared these latest observations of the TW Hydrae disc to Hubble observations made several years ago. ...

• Astrophysical Journal 948(1):36 (2023 May 01) DOI: 10.3847/1538-4357/acbdf1 (pdf)