TAU-US team discovers new extrasolar planet

Astronomers use Einstein's Theory of Relativity to discover a planet outside our solar system, named Kepler-76b.

By JUDY SIEGEL-ITZKOVICH
Kepler-76b illustration 370 (photo credit: Courtesy of TAU)
Kepler-76b illustration 370
(photo credit: Courtesy of TAU)
Around a century after the publication of Albert Einstein’s Theory of Relativity, a team of astronomers from Tel Aviv University and from the Harvard-Smithsonian Center for Astrophysics (CfA) has discovered a planet outside our solar system using a method based on the great physicist’s ideas.
For that reason, Prof. Tsevi Mazeh, doctoral student Simchon Faigler from TAU’s School of Physics and Astronomy and their American colleagues have dubbed the Jupiter-sized sphere “the Einstein Planet.”
The extra-solar planet – officially named Kepler-76b by the US National Aeronautics and Space Agency – is the first-ever to be discovered using the “induced relativistic beaming” of light from the host star.
For the past two years, Mazeh and Faigler have been searching for planets around other stars using a novel detection method. Their technique is based on identifying three very small effects that occur simultaneously as a planet orbits a star.
The first effect is Einstein’s relativistic beaming effect (also known as Doppler beaming) that causes a star to brighten and dim as it is tugged back and forth by an orbiting planet.
Detection of planets via the beaming effect was predicted in 2003 by Prof. Avi Loeb of Harvard University and Prof.
Scott Gaudi (now at Ohio State University).
The second effect that the Faigler-Mazeh method looks for is the stretching of a star into a football shape by the gravitational tides raised by an orbiting planet. Such distorted stars appears brighter when observed from the side due to the larger visible surface area; they appear fainter when viewed end-on.
The third, minor effect is due to starlight reflected by the planet itself.
Because the variations in brightness are extremely small (in the order of one part per 10,000), these effects can be detected only with accurate data gathered by space missions.
The TAU team, supported by a European Research Council Advanced Grant, analyzed data on more than 100,000 stars obtained by NASA’s Kepler mission for evidence of the beaming and the other two modulations.
After potentially discovering a planet, the Israeli scientists collaborated with Dr. David Latham from the CfA and his team – which includes Dr. Lars Buchhave – to observe the planetary candidate from the ground for additional spectroscopic confirmation.
A year ago, Faigler and Mazeh noticed the three effects in one of the stars observed by Kepler. Ground-based observations to confirm detection of the planet were performed by Latham and his team at the Whipple Observatory in Arizona, and by Lev Tal-Or, another TAU doctoral student, at the Haute-Provence Observatory in France. Both telescopes unequivocally confirmed the existence of the planet, now called Kepler-76b.
Last week, Faigler, Tal-Or, Mazeh, Latham and Buchhave announced the discovery in a paper to be published in the Astrophysical Journal.
Kepler-76b, part of the constellation Cygnus, is at a distance of about 2,000 lightyears from Earth. The planet, with a mass double that of Jupiter, orbits its parent star very closely, with a period of one-and-a-half days.
Because the orbit is so “close,” the planet is probably “locked” so that the same side of the planet faces the star at all times. That part of the planet would be heated by stellar radiation.
Carefully examining the stellar brightness, the team found strong evidence that the heat absorbed by the planetary atmosphere is carried around the planet by jet-stream winds for about 16,000 kilometers – a substantial fraction of the planetary circumference.
Such an effect has been observed before only via infrared imaging with NASA’s Spitzer Space Telescope. This is the first time such a wind effect has been observed in the optical band. The study of such jets is extremely important for understanding how planetary atmospheres respond to intense stellar heating, Mazeh said.
All of the planets found so far by the NASA Kepler mission were discovered because they transit (eclipse) their parent stars. What is special about the new technique is that it can locate even non-transiting planets.
“The irony is that Kepler-76b is in fact transiting the edge of its parent star,” said Faigler.
“This is why originally it was misclassified as an eclipsing binary. Only through detection of the three small effects were we able to determine that it is actually a planet.
“This is the first time that this aspect of Einstein’s Theory of Relativity has been used to discover a planet,” noted Mazeh, who is a participating scientist in the NASA Kepler mission.
“We have been searching for this elusive effect for more than two years, and we finally found a planet! It is amazing that already a decade ago Loeb and Gaudi foresaw this happening.
“Shay Zucker of TAU, a former student of mine, called my attention to this prediction,” continued Mazeh.
“At first, I did not believe it is possible, but I slowly got into it. Luckily, we got the support of the European Research Council to carry this project forward, and we collaborated with Dave Latham who believed in this project and kept following the false candidates that Simchon and I were giving him,” Mazeh said. “In the end we found Kepler-76b! It is a dream come true.”
“The discovery proves the feasibility of the method,” said Faigler. “We hope to find more planets like Kepler-76b using the same technique. This is possible only because of the exquisite data NASA is collecting with the Kepler spacecraft for more than 150,000 stars.”


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