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.