Scientists Found That Protoplanetary Disks Around Wide Binaries Have Strange Orientations

Astronomers have been searching the skies using the Atacama Large Millimeter/submillimter Array (ALMA) to study orbital geometries and protoplanetary disks that surround binary stars. The team found that protoplanetary disks orbiting most compact binary star systems have very nearly the same orbital plane. However, when a protoplanetary disk orbits a wide binary pair, the orbital plane tends to be severely tilted.

Scientists believe that observations can help teach us about planet formation and complex environments. Scientists say that they already know that the orbits of binary stars can warp and tilt the disk around them. That results in a disk that is misaligned relative to the orbital plane of its host star. Team says that it wanted to learn more about typical geometries of the protoplanetary disks that form around binary stars, known as circumbinary disks.

The team set out to learn more about typical geometries of such protoplanetary disks. In the research, the astronomers compared ALMA data of the circumbinary disks with a dozen so-called "Tatooine" planets (planets orbiting binary stars) found using the Kepler space telescope. What the team discovered was that the degree that binary stars and their circumbinary disks are misaligned is very much dependent on the orbital period of the stars. Stars with shorter orbital periods tend to have the disk in line with its orbit.

The team found that binary stars with orbital periods that were longer than a month typically have misaligned circumbinary disks. The team found a clear overlap between small disks, orbiting compact binaries, and the circumbinary planets that were found with the Kepler mission. The team also notes that it's the Kepler mission lasted only four years, the astronomers were only able to discover planets around binary stars orbit each other in fewer than 40 days.

The team now wants to determine why they're such a strong correlation between disk misalignment and binary star orbital period. The scientists hope to use the ALMA and Very Large Array to study disk structures at higher levels of precision. That will allow them to study how worked or tilted disks impact planet formation.