An artist’s rendering of the Kepler-16 system, depicting Kepler-16b orbiting binary stars. Credit: Illustration courtesy of Amanda Smith
A team of astronomers, including a researcher from Ohio State, located a planet orbiting two stars that resembles the planet Tatooine from the movie series “Star Wars.”
Using a technique known as the radial velocity method — a way to detect planets outside Earth’s solar system, also known as exoplanets — researchers found Kepler-16b, a gas giant orbiting two sun-like stars about 245 light-years from Earth, according to NASA. Although a NASA telescope discovered it in 2011, the Feb. 25 study marks the first time a circumbinary planet — a planet orbiting two stars — was located using this method.
David Martin, NASA postdoctoral fellow at Ohio State and co-author of the paper, said the results are an essential step toward locating new exoplanets in binary star systems — solar systems where two stars are in orbit.
“We are trying to find brand-new planets, but we also want to test that our methodology works,” Martin said. “So this was a system that was a perfect test.”
Scott Gaudi, Thomas Jefferson Professor for Discovery and Space Exploration at Ohio State who did not take part in the study, said astronomers have previously identified circumbinary planets using the transit model, which monitors light coming from stars to detect exoplanets. However, he said this can be difficult as it requires a very specific alignment in the observer’s line of sight.
Gaudi said this is why the method used in the study is much more effective in detecting planets like Kepler-16b.
“With radial velocity, none of those alignments are required, and thus many more systems can potentially be discovered,” Gaudi said. “As circumbinary systems teach us a lot about planet formation, this is a very exciting result.”
The radial velocity method is based on the Doppler effect, suggesting the frequency of waves increases or decreases depending on if an object is moving toward or away from an observer, Martin said. Radial velocity involves observing shifts in a star’s spectra data, information that records light emitted by a star, to detect movement caused by the gravitational pull of orbiting planets.
Martin said the radial velocity method has not historically been used to find circumbinary planets because the stars move differently than those in single star systems due to their proximity to one another. He said even when researchers knew a system had two stars, it was difficult to detect if there were planets in the system.
“The two stars are just orbiting each other. They go on this huge motion, and the amplitude of that motion will be tens of kilometers per second,” Martin said. “You have to try and find something that’s three, four orders of magnitude lower. So you’re really looking in the weeds of the signal.”
Martin said researchers got around this issue by looking at a system in which one of the two stars was significantly brighter. He said they looked at a binary system where one star was about 50-100 times brighter than the other, effectively making it seem like all the light in the system was coming from one source instead of two.
“Right now we’re sneaky,” Martin said. “We try to get stars with very different brightnesses. But it would be nice to be able to do it when you have similar brightness things because that would open the door to looking at many more binaries.”
