In Star Wars, a young Skywalker steps out onto the surface of Tatooine and watches the setting of two suns. This may be what it is like for life forms on the rocky planet known as Kepler-16, which is in a star system. An international team of astronomy recently confirmed that this planet is a circumbinary planet, which means that it is both a star and a planet at the same time.
The international team is led by Professor Amaury Triaud of the University of Birmingham. The campaign began in 2013 and relied on telescopes from around the world to conduct radial velocity surveys. Monthly Notices of the Royal Astronomical Society is where the research is published.
The planet is located approximately 245 light-years from Earth and has a period of 228.6 days. Life forms on this planet would look up into the sky and see two suns setting. The planet is outside its two stars, meaning that the surface is likely to be very cold. The transit method was used to discover it. The photometry is transit.
Astronomers observe stars for dips in brightness that show the presence of planets. Astronomers rely on this method because it establishes constraints on an exoplanet's size. The team relied on the SOPHIE echelle spectrograph to perform their study. The system has measurement on it.
The method consists of observing stars for signs of iwobble, which indicates that the forces of gravity are acting on them. Aix-Marseille University researcher Dr. Alexandre Santerne is one of the co-author's.
“Kepler-16b was first discovered 10 years ago by NASA’s Kepler satellite using the transit method. This system was the most unexpected discovery made by Kepler. We chose to turn our telescope to Kepler-16 to demonstrate the validity of our radial-velocity methods.”
The finding that the stars are in the same location may help resolve an open question about the stars. A disk of dust and gas surrounding young stars is believed to form planets according to the most widely-accepted model of planet formation. The model predicts that the forces of gravity might interfere with planet formation, which presents some difficulties for the systems concerned.
The discovery and statistical significance of hot Jupiters have raised questions. Gas giants can't form close to their stars due to insufficient mass and excessive heat. The only possible explanation is that planets migrate within the disk as a result of interactions with other bodies.
Disc-driven migration is a relatively common process according to these findings. Said Prof. Triaud.
“Using this standard explanation it is difficult to understand how circumbinary planets can exist. That’s because the presence of two stars interferes with the protoplanetary disc, and this prevents dust from agglomerating into planets, a process called accretion.
“The planet may have formed far from the two stars, where their influence is weaker, and then moved inwards in a process called disc-driven migration – or, alternatively, we may find we need to revise our understanding of the process of planetary accretion.”
The detection of Kepler-16b using a ground-based telescope was significant. It demonstrated that it is possible to detect circumbinary planets using more traditional methods with greater efficiency and lower costs than space-based observatories. The team plans to continue searching for previously unknown circumbinary planets and answer questions about planetary formation.
Dr. Boisse is the scientist in charge of the SOPHIE instrument at Aix-Marseille.
“Our discovery shows how ground-based telescopes remain entirely relevant to modern exoplanet research and can be used for exciting new projects. Having shown we can detect Kepler-16b. We will now analyze data taken on many other binary star systems and search for new circumbinary planets.”
Further reading is done by the Royal Astronomical Society.
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