Free Astronomy Magazine July-August 2023

23 JULY-AUGUST 2023 ASTRO PUBLISHING more, Maryland, compared these latest observations of the TW Hy- drae disc to Hubble observations made several years ago. “We found out that the shadow had done something completely differ- ent,” said Debes, who is principal in- vestigator and lead author of the study published in The Astrophysical Journal . “When I first looked at the data, I thought something had gone wrong with the observation because it wasn’t what I was expecting. I was flummoxed at first, and all my col- laborators were like: what is going on? We really had to scratch our heads and it took us a while to actu- ally figure out an explanation.” “We hatched a theory of what might be causing the changing shadows,” added Rebecca Nealon, a member of the science team at the University of Warwick in the United Kingdom. “But to test this we had to run so- phisticated models where we varied the number of discs and their orien- tations to try to reproduce Hubble’s observations.” The best solution the team came up with is that there are two mis- aligned discs casting shadows. They were so close to each other in the earlier observation they were missed. Over time they’ve now sep- arated and split into two shadows. “We’ve never really seen this before on a protoplanetary disc. It makes the system much more complex than we originally thought,” said Debes. T his illustration is based on NASA/ESA Hubble Space Telescope images of a gas and dust discs encircling the young star TW Hydrae. Hubble photos show shad- ows sweeping across the discs encircling the system. The interpretation is that these shadows are from slightly inclined inner discs that block starlight from reaching the outer disc, and therefore cast a shadow. The discs are slightly inclined to each other because of the gravitational pull of unseen planets warping the disc structure. [NASA. ESA, L. Hustak (STScI)]