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.
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