Free Astronomy Magazine May-June 2020

atooine’ planetary disks 45 MAY-JUNE 2020 SPACE CHRONICLES that Kepler would have a hard time finding. “With our study, we now know that there likely isn’t a large population of misaligned planets that Kepler missed, since circumbi- nary disks around tight binary stars are also typically aligned with their stellar hosts,” added Czekala. Still, based on this finding, the as- tronomers conclude that mis- aligned planets around wide binary stars should be out there and that it would be an exciting population to search for with other exoplanet- finding methods like direct imaging and microlensing. (NASA’s Kepler mission used the transit method, which is one of the ways to find a planet.) Czekala now wants to find out why there is such a strong correlation be- tween disk (mis)alignment and the binary star orbital period. “We want to use existing and coming facilities like ALMA and the next generation Very Large Array to study disk struc- tures at exquisite levels of preci- sion,” he said, “and try to under- stand how warped or tilted disks af- fect the planet formation environ- ment and how this might influence the population of planets that form within these disks.” “This research is a great example of how new discoveries build on pre- vious observations,” said Joe Pesce, National Science Foundation Pro- gram Officer for NRAO and ALMA. “Discerning trends in the circumbi- nary disk population was only made possible by building on the founda- tion of archival observational pro- grams undertaken by the ALMA community in previous cycles.” T wo examples of aligned and misaligned protoplanetary disks around binary stars (circumbinary disks), observed with ALMA. Binary star orbits are added for clarity. Left: in star system HD 98800 B, the disk is misaligned with inner bi- nary stars. The stars are orbiting each other (in this view, towards and away from us) in 315 days. Right: in star system AK Sco, the disk is in line with the orbit of its binary stars. The stars are orbiting each other in 13.6 days. [ALMA (ESO/NAOJ/NRAO), I. Czekala and G. Kennedy; NRAO/AUI/NSF, S. Dagnello] !