A stream of gas falling into a triple-star system in the Orion constellation reveals how planets can end up tilted relative to their stars, according to a new astronomical study.
"If these streamers are common, then we can naturally explain why planets may not necessarily end up in very orderly systems. They can have much more random orientations," said Jaehan Bae , Ph.D., a professor of astronomy at the University of Florida who helped lead the new study.
At issue is how planetary orbits are aligned with the stars they circle. While our own solar system has all eight planets orbiting the sun's natural orientation, many other planetary systems in the galaxy have much more tilted angles. That includes GW Orionis, the triple-star system at the heart of this new study.
Imagine three hula hoops hanging in space, one inside another. The typical expectation is all three hoops would be at the same angle, as if they are simply lying on the ground nested one inside another. Around GW Orionis, however, each hoop is tipped at a different angle.
The new study suggests an incoming river of gas gradually tilted the outer hoop, while leaving the inner one mostly unchanged, causing the rings to be misaligned with each other. If those rings form planets, the planetary orbits would end up tilted to one another as well.
The study was led by Maria Galloway-Sprietsma, a doctoral student in Bae's group. The team, which included co-authors from the Max-Planck Institute for Astronomy in Germany, Ireland's University of Galway and Queen Mary University of London, published their findings Aug. 6 in The Astronomical Journal.
Astronomers had previously noticed the misaligned rings of GW Orionis, but most theories chalked up the out-of-kilter rings to the influence of the three stars in this triple system. However, when reviewing data collected by the Atacama Large Millimeter/submillimeter Array telescope in Chile, Bae's group realized that this large stream of gas better explained how the planetary disks had come out of alignment.
"What we need next is a systematic survey of young stars to see how many have streamers and how many don't," Galloway-Sprietsma said. "That will tell us how important they are in shaping planetary systems."
