Scientists catalog all known planet-hosting, three-star systems

Possible orbits of a planet in a hierarchical triple-star system. Note that m1, m2, and m3 do not necessarily agree. Credit: The Astrophysical Journal Supplement Series (2022).

Manfred Cuntz, a planetary physicist at The University of Texas at Arlington, has been leading a project that records all known systems where three or more stars have planets.

The study, called “An Early Catalog of Planet-hosting Multiple-star Systems of Order Three and Higher,” is like a library of these systems.

This work was published in The Astrophysical Journal Supplements Series, with contributions from several other scientists, including some graduates of the University of Texas at Arlington.

The research considers various factors, including the types of orbits the planets take around their stars.

The team also looked at previous disagreements about what makes a system a triple-stellar one.

Most planets, including those in our solar system, revolve around one star. However, about 100 known planets belong to ‘stellar binaries’ or systems with two stars.

Cuntz noted, “The number of planets that belong to systems with three or four stars is quite small—about 40, with the exact number varying based on some controversial or unconfirmed cases.”

Cuntz shared that there are about 30 confirmed planets in triple-stellar systems, which makes up only 0.5% of all identified planets. That’s what makes these planets so unique.

The NASA Kepler Space Telescope, which was active from 2009 to 2018, helped to discover these triple-stellar systems with planets.

Scientists expect that with the James Webb Space Telescope, which launched in 2021, they will be able to identify even more of these systems.

Most planets in triple-stellar systems are gas giants, like Jupiter. Also, the stars in these systems are relatively large compared to regular stars. But, there have been some Earth-sized planets found too.

In a triple-stellar system, there are usually two stars that are very close together and orbit each other, and a third star orbits this pair from a greater distance. Systems with more than three stars are likely to have even more complex orbits.

According to Cuntz, the existence of planets in triple-star systems is quite difficult to explain from a scientific point of view, especially regarding how they form and how they maintain stable orbits. He added, “These topics are a strong motivation for future research at UTA, which will also involve students.”

Source: University of Texas at Arlington.