When we look into the sky and see a single Sun, many don’t realize that our solar system is unique in its arrangement. Typically, stars that look like our Sun are born with siblings. In the solar systems with multiple stars, planets typically have orbits that aren’t aligned with the orbits of their stars. The strange orbits originate in the planet-forming disks surrounding the stars.
A new study from two independent teams of astronomers using ALMA (Atacama Large Millimeter/submillimeter Array) have looked at data on a triple star system called GW Orionis. The system is very young and has three stars with the inner stars called GW Ori A and B, separated by 1 au in the third star called GW Ori C, which orbits the other two stars at approximately 8 au.
ALMA discovered three separate rings with different orientations in the massive planet-forming disk of the star system. The rings are located roughly 46, 185, and 340 au from the star system center. The inner ring is very misaligned relative to the outer rings and the three stars. The outermost ring is the largest planet-forming disk ever observed.
Astronomers say that a planet forming in the gap between the inner and outer ring would be incredibly far away from the stars. To get an idea of just how far away a planet would be in a ring 340 au from the host stars, consider that Neptune is only about 30 au from the Sun. ALMA first observed the misalignment of the rings in 2017.
Scientists have mapped the orbits using telescopes operating at infrared wavelengths for over 11 years, covering a full orbital period. Both of the teams of astronomers have performed computer simulations to determine what could’ve caused the inner ring to be misaligned from the rest of the disks and the stars. Misalignments have been linked to a “disk-tearing effect,” suggesting that the gravitational pull of the stars in different planes can warp and break their disks. One researcher says that the inner ring contains enough dust to build 30 Earths, which is sufficient for a planet to form in the ring.