Yale researchers and collaborating citizen scientists have discovered a new astronomical phenomenon — a planet that revolves around twin suns while at the same time being orbited by a second pair of stars.
This planet, called PH1, is the seventh circumbinary planet — a planet that orbits two stars — that has been discovered, said Megan Schwamb, Yale physics postdoctoral fellow. The presence of a second pair of revolving stars makes PH1’s discovery entirely unique, as it is the first identified circumbinary planet in a four-star system. Schwamb and her team of researchers announced the discovery of PH1 at an annual meeting of the Division for Planetary Sciences of the American Astronomical Society in Reno, Nev. on Oct. 15.
Schwamb, the lead author of the paper, said PH1 can help scientists understand planet formation.
“If we want to understand how planets form in a solar system like ours, we need to understand the extremes,” she said. “This is the end case of planet formation because of the impulses and gravitational pulls of four interacting stars.”
Yale astronomy professor Debra Fischer said this discovery increases the chances of finding life on other worlds. Even if there’s no sign of life on PH1, the fact that a planet could be made under such challenging circumstances indicates that there are many more planets in the universe, some of which could sustain life, she said. PH1, she added, will prompt scientists to “revise our model for planet formation and accept that it’s a much more robust process that we ever guessed.”
PH1 was discovered with the help of Yale’s Planet Hunters, an organization Fischer helped launch in 2010. Planet Hunters is Yale’s experiment in citizen science, a new approach to astronomical science that takes advantage of “excellent human pattern recognition skills,” said Chris Lintott of Zooniverse, a collection of citizen science projects that includes Planet Hunters.
Volunteers search for irregularities in the data, mostly measurements of star brightness graphed into light curves from the NASA Kepler space mission, Fischer said. Unlike humans, computers need a precise algorithm to identify data irregularities, she added.
Volunteers Kian Jek of the University of California and Robert Gagliano of the University of Arizona discovered PH1 when they noticed a “regular blip” in the “absolutely crazy” light curve data for the twin suns, which led them to suspect the presence of a third body, Fischer said.
Jek and Gagliano reported their observations to Planet Hunters, and Schwamb then assembled a team of 10 astronomers to follow up. Schwamb’s team looked at radiovelocity data from telescopes stationed in Hawaii and determined PH1, a gas giant with a radius 6.2 times that of the earth, is slightly larger than Neptune. The team also noticed a “wobble effect” generated by the smaller, more distant stars, which allowed them to calculate the distance between the four stars and PH1, Schwamb said. Using this data, the team was able to conclude PH1 exists in a four-star system.
Schwamb called each new circumbinary planet a “real gem” for what it contributes to the study of planet formation.
“We hope to find smaller and smaller planets and more systems with more than one planet,” said Jerome Orosz GRD ’96, who worked with Schwamb on the paper presenting PH1.
Professors of physics and astronomy recognize the impact this discovery could have on their field in the coming years. Princeton professor Lucianne Walkowicz said knowledge of extrasolar planetary systems is changing rapidly, adding that PH1 is just one more piece of new information that sends scientists “back to the drawing board to revise theories.”
Yale astronomy professor Sarbani Basu said this discovery shows how unexpected the field can be. She added that she hopes PH1 will encourage astronomy curricula to pay more attention to stellar dynamics, the statistical study of the motion of stars due to mutual gravity.
Schwamb’s next goal in the study of circumbinary planets is to continue encouraging citizen science and looking for these “rare gems.”
“We know we can do it, we’ve done it and now we’ll see what we can say about the whole population of these planets,” Schwamb said.
The paper has been submitted for publication to the “Astrophysical Journal.”