Triple-stellar systems have two stars orbiting one another with a third orbiting the pair. Now we have a catalog containing all known three-star systems that also host planets around them.
This artistic impression shows the view from the exoplanet Gliese 667Cd looking towards the parent star (Gliese 667C). In the background to the right, the more distant stars in this three-star system (Gliese 667A and Gliese 667B) are visible. Image credit: ESA/NASA
A planetary physicist at The University of Texas at Arlington is the lead author of a study that catalogs all known planet-hosting, triple-stellar systems—those having three or more stars with planets.
Manfred Cuntz, professor of physics, led the project titled “An Early Catalog of Planet-hosting Multiple-star Systems of Order Three and Higher.” This study provides a thorough bibliographic assessment of planet-hosting, triple-stellar, or three-star systems.
It was recently published in The Astrophysical Journal Supplements, a journal of the American Astronomical Society that has one of the highest impact factors in the field. Co-authors include UTA alumni G.E. Luke, Matthew Millard and Lindsey Boyle, and Shaan D. Patel, a doctoral-bound graduate student.
An artist’s impression of sunset on an austere exoplanetary landscape, in this case of the super-Earth Gliese 667 Cc. The exoplanet resides in a triple star system and the three suns are visible in the sky. Credit: ESO/L. Calçada
The paper offers a system classification that considers the various types of planetary orbits, among other factors. Additionally, the authors examine past controversies and planet retractions based on the criteria for what constitutes a planet-hosting, triple-stellar system.
Most planets, such as all in Earth’s solar system, orbit a single star. About 100 known planets are members of stellar binaries, the authors wrote in their study. And a small number orbit three-star formations.
“The number of planets found to be hosted by higher-order systems is relatively small—about 40 for triple and quadruple systems combined, with the exact number depending on whether some controversial or unconfirmed cases are included,” Cuntz said.
“The number of confirmed planets in triple-stellar systems currently stands at about 30, which is approximately 0.5% of the total number of planets identified. This aspect makes those planets very special.”
This illustration depicts NASA’s exoplanet hunter, the Kepler space telescope. Kepler left a legacy of more than 2,600 exoplanet discoveries. Credits: NASA/Wendy Stenzel/Daniel Rutter
The NASA Kepler Space Telescope, operational from 2009-18, aided in discovering planet-hosting,three-star systems, Cuntz said. Scientists expect the number of known systems to increase, particularly with the abilities of the James Webb Space Telescope, which was launched in 2021.
The authors note that the overwhelming majority of triple-stellar system planets are Jupiter-type, meaning they are gas giants, and the host stars are relatively massive, compared to typical main-sequence stars. However, some Earth-mass planets have been found as well.
Triple-stellar systems can be divided into two subgroups, each of which travels in a relatively large orbit around the system’s center of mass.
In a three-star system, two of the stars usually form a close binary pair (two stars that are gravitationally bound to and in orbit around each other), and the third orbits that pair from a farther distance. Systems with more than three stars are expected to produce even more complicated orbiting arrangements.
“The existence of planets in triple-star systems is extremely challenging theoretically, both regarding their formation and orbital stability,” Cuntz said. “These topics are a stark motivation of future UTA research, also involving students.”
Source: University of Texas at Arlington
