Worlds With Multiple Suns Abundant
A computer simulation of a Jupiter-sized clump of matter swirling around a binary star system and on its way to becoming of a giant gas planet.
Credit: Alan Boss/Carnegie Institution's of Terrestrial Magnetism

WASHINGTON, D.C.--Two new studies suggest that planet formation around multiple star systems may be more common than previously thought.

The findings were presented here at the 207th meeting of the American Astronomical Society.

One study, lead by doctoral student Deepak Raghavan from Georgia State University, confirmed that 29 planet-harboring star systems also contained a second star; three actually had two companions and were triple star systems.

Raghavan and his team combed through archived star data to identify 131 star systems with planets that scientists had previously suspected of having companion stars. They then used telescopes at the Cerro Tololo Interamerican Observatory in Chile to confirm the results and to also look for new systems with multiple stars.

The group found one previously unknown stellar companion around HD 38529, a star known to have planets but until now was thought to be a single star system.

Computer agrees

Theorists have long wondered if such setups could occur, given the complex gravitational situations involved.

But in a separate new computer modeling effort, Alan Boss at Carnegie Institution's Department of Terrestrial Magnetism (DTM) and colleagues determined that gas-giant planets like Jupiter can indeed form in binary star systems in much the same way that planets form around single stars such as the Sun.

"We tend to focus on looking for other solar systems around stars just like our Sun," Boss said. "But we are learning that planetary systems can be found around all sorts of stars."

It was once thought that the strong gravitational forces from stars in double star systems interfered with each other's ability to form planets.

But the new theoretical model by Boss' team shows that if the gravitational force from one star in a double star system is weaker than the other, then gas-giant planets can form in much the same way as they do around single stars.

In these theoretical systems, the whirling disks of dust and gas that form the starting material for planets could remain cool enough to grow into solid cores and form gas planets with masses thousands of times that of Earth.

In this line of thinking, the planet-forming disk condenses into dense spiral arms, within which the dust and gas clump together to eventually form planets. The process is believed to require less than 1,000 years--much shorter than previously thought by many astronomers, though Boss has for years now been modeling similar brief time spans for giant planet formation around single stars.

Other Earths?

The model also suggests that there would be plenty of room for Earth-like planets to form close to the central star after the gas giants finished developing.

"This result may have profound implications in that it increases the likelihood of the formation of planetary systems resembling our own," Boss said.

That's because binary star systems tend to be rule rather than the exception in our galaxy. It's estimated that up to two out of every three stars in the Milky Way are part of multiple star systems, many of them binary. If such systems can shelter both outer gas giant planets as well as inner Earth-like planets, then the odds of finding habitable planet in distant star systems would be increased by roughly threefold.

The team's findings will also be published in an upcoming issue of the journal Astrophysical Journal.