Binary stars said to fling off planets

Planets around widely spaced binary stars are susceptible to violent disruptions, more so than if the stars were closer to each other, U.S. researchers say. Scientists at Northwestern University said they conducted 3,000 computer simulations to study the effects of binary stellar companions -- some with tight orbits around each other and others with wide or distant orbits -- on the formation and evolution of planetary systems. The results showed wide binary stars in planetary systems can lead to dramatic events over time, including the ejection of large planets from the systems in over half the computer simulations, a Northwestern release said Monday. The findings are strong evidence this process occurs regularly in known extrasolar planetary systems, the researchers said. Many stars are members of binary star systems, where two stars orbit each other, planetary systems around the cosmic pair can be altered by the gravity of the stars. "The stellar orbits of wide binaries are very sensitive to disturbances from other passing stars as well as the tidal field of the Milky Way," said Nathan Kaib of the Northwestern department of physics and astronomy. This can have dire consequences for planets in these systems since the gravity of a close-passing star can radically change planetary orbits around the other star, causing planets to scatter off of one another and sometimes get ejected to interstellar space, the scientists said.