A team of European astronomers has stumbled upon a family gathering in space: twin stars in a binary system, each hosting Jupiter-sized exoplanet “cousins.” The exciting discovery was made while a team of British, Swiss and Belgian scientists were studying a star called WASP-94A. They first found evidence for the presence of a “hot Jupiter” exoplanet around this host, and then while continuing to probe this system, they accidentally discovered another star. Further investigation then revealed that this newly discovered star, dubbed WASP-94B, also hosted a hot Jupiter of its own. The work has been published in Astronomy and Astrophysics.
Binary systems-- two stars orbiting each other-- are surprisingly common in space; it’s estimated that as many as half the stars in our Milky Way are part of a binary system. Although it was initially thought that companion stars could affect planet formation, a recent study found that stars with exoplanets are just as likely to be part of a binary system. However, it was not until 2012 that the first example of multiple planets orbiting two host stars was discovered. Now, as part of the WASP-South survey, astronomers discovered another example of these intriguing systems.
The new exoplanets are both a type of planet called a hot Jupiter. These planets reside much closer to their host than our own gas giant and their years are significantly shorter than Earth’s, lasting just a few days. These planets are also fairly rare, so the chances of discovering two orbiting stars in a binary system were slim. It’s therefore possible that WASP-94 provides the ideal conditions for these unusual planets, making it a useful tool for understanding why hot Jupiters hug their hosts so tightly.
These gas giants have mystified astronomers for many years because they shouldn’t be able to form so close to their host; It is simply too hot. Scientists therefore reasoned that they must form much further out, where it is cool enough for ice to freeze out of the whirling protoplanetary disk of dust and gas that surrounds newly formed stars. After the planet is born in this spinning disk, something must drag it closer to the host star. One possibility is that the interaction with another planet or star can cause this to happen. Researchers may therefore be able to use this newly discovered system to study this process.
“WASP-94 could turn into one of the most important discoveries from WASP-South,” study author Coel Hellier said in a news-release. “The two stars are relatively bright, making it easy to study their planets, so WASH-94 could be used to discover the compositions of the atmospheres of exoplanets.”
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