Astronomers have reported a discovery that the majority of circumbinary planets – planets that orbit two stars, like Luke Skywalker's home planet Tatooine in the fictitious Star Wars universe – form away from their hosts and then migrate into orbit.
There are few environments more extreme for planet formation than
a binary star system, in which the stars are so close that the
interacting gravity of the pair causes them to orbit about a
common center of mass.
Gravitational interactions between the stars and planets cause collisions of protoplanetary material complicating the process of planet formation, and making it very unlikely. Astronomers explained the existence of such planets in a study published in Astrophysical Journal Letters this week.
Researchers from the University of Bristol used computer models to simulate circumbinary planets’ formation in the Kepler-34 system - an eclipsing binary star system in the Milky Way constellation of Cygnus - observed by the Kepler space telescope.
"Our simulations show that the circumbinary disk is a hostile environment even for large, gravitationally strong objects. Taking into account data on collisions as well as the physical growth rate of planets, we found that Kepler 34(AB)b [a Saturn-sized gas giant discovered in 2012 by NASA's Kepler mission] would have struggled to grow where we find it now”, said Z. M. Leinhardt, one of the authors of the study, according to the press-release.
Based on this astronomers concluded that such planets form away from the twin stars, and then migrate to another location. However they said that a possible exception may be Kepler-47 (AB)c which is further away from the host stars than any other planets in the Kepler-34 system.
"Circumbinary planets have captured the imagination of many science-fiction writers and film-makers - our research shows just how remarkable such planets are. Understanding more about where they form will assist future exoplanet discovery missions in the hunt for earth-like planets in binary star systems”, said Stefan Lines, lead author of the study.