SBU Astrophysicist Has New Theory on Free-Floating Binary Planets

This AI-produced image depicts free-floating exoplanets in outer space. Credit: Yihan Wang

Exoplanets are planets beyond our solar system, with more than 5,000 identified so far. They are expected to form and orbit around stars, in a similar fashion to planets in our solar system.

However, some of these planets appear "free-floating" in space, not bound to any host star. The puzzle to their formation was further deepened in fall 2023, when astrophysicists using the James Webb Space Telescope identified massive floating binary objects about the size of Jupiter - and dubbed them JuMBOs (Jupiter-mass binary objects).

Astrophysicists have been puzzled by these reported new objects. But Stony Brook University astrophysicist Rosalba Perna, and colleagues Yihan Wang and Zhaohuan Zhu from UNLV proposed a new theory. In a paper published in Nature Astronomy, they showed via N-body simulations, a common tool to describe the dynamic of cosmic particles, that JuMBOs can be formed as the result of ejection after a close flyby with another star.

"These exoplanets cannot be easily explained by standard theories of planetary formation," said Perna, a professor in the Department of Physics and Astronomy. "Our recent work highlights stellar interactions as an important factor in the development of unusual planetary systems in dense stellar environments, and it suggests free-floating binary planets may be formed in such regions."

Perna said the idea based on the theory that two planets are originally in outer orbits of a planetary system. "Our simulations demonstrate that close encounters can lead to a 'kick'," added Wang, "resulting in the ejection of a pair of giant planets, a fraction of which remains bound and gives rise to JuMBOs".

The research leading to this theory and the paper are supported in part by the National Science Foundation, NASA, and the Nevada Center for Astrophysics.

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