Astronomers have discovered the first candidate exoplanet with a polar multi-orbit. Its existence could explain the gap in the circumpolar binary disk surrounding the AC Hercules binary system. A preprint of this study is available at arXiv.org. Many stars in the post-asymptotic giant divergence stage of evolution have stable disks observed in binary systems, surrounding both stars (peribinary disks), with masses up to 0.1 solar masses and sizes up to 1000 astronomical masses. It is characterized by unit.

Such structures may form from stellar wind material during interstellar mass transfer processes, or from common envelope material, suggesting that such a disk is surprisingly similar to the protoplanetary disk of a young star. The similarities are interesting. A team of astronomers led by Rebecca G. Martin from the University of Nevada reported finding evidence for polar-orbiting exoplanets in the circumbinary disk of the AC-Hercules binary star system. The researchers looked for the best model that could explain the size, structure, and mass of the observed disks.

AC Hercules consists of a post-asymptotic giant branch star with a mass of 0.73 solar masses and a companion star with a mass of 1.4 solar masses, and is located approximately 4,200 light-years from the Sun. The semi-major axis of the binary system’s orbit is 2.83 AU. The star is surrounded by a disk consisting of two parts separated by a gap. The inner disk is dust-poor and extends from 4.5 to 19.8 AU from the binary star. The outer disk contains both gas and dust. Scientists discovered that the disk is tilted 96.5 degrees to the binary star, making it the first polar binary disk to orbit a binary star system containing stars that are far from the main sequence.

At the same time, the disc’s polar configuration alone cannot explain the gap. A much better model is a giant planet with an orbital radius of about 22.6 AU. It may be a second-generation planet that formed from material ejected by an evolved star. The researchers also hypothesize that the circumbinary disk was previously largely undisplaced relative to the binary system, and that tidal influences caused it to become polar. Furthermore, it is now thought to be expanding gradually, and the expansion phase will be longer than the star’s post-red giant evolution phase.

source: https://arxiv.org/abs/2310.19600