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Astronomers take a second look at twin star systems

Apples-to-apples comparisons in the distant universe are hard to come by. Whether the subject is dwarf galaxies, supermassive black holes, or "hot Jupiters," astronomers can spend months or years searching for comparable objects and formations to study. And it is rarer still when those objects are side-by-side.

But a new Yale study offers a road map for finding "twin" planetary systems—showing whether binary stars that orbit each other, and that were born at the same time and place, tend to host similar orbiting planets. The study's authors found that certain orientations of twin star systems may provide critical information about planet formation, while also making it easier for astronomers to discover planets within the systems.

The side-by-side, "edge on" configuration of certain binary star systems potentially allows astronomers to do comparative studies, in the same way that doctors study human twins to gain knowledge about biological and behavioral mechanisms.

"This could be an unprecedented avenue for examining how deterministic, or orderly, the process of planet formation is," said Malena Rice, an assistant professor of astronomy in Yale's Faculty of Arts and Sciences and senior author of the new study.

The study in The Astrophysical Journal Letters. The first author is Joseph Hand, an undergraduate at the University of Kansas who conducted the research as a Dorrit Hoffleit Undergraduate Research Scholar, a Yale fellowship named in honor of the longtime Yale astronomer. Konstantin Gerbig, a Ph.D. candidate in Yale's Graduate School of Arts and Sciences, is co-author of the study.

In earlier work, Rice identified an unexpectedly large number of binary systems with orbits that are perfectly aligned, meaning that the two binary stars and their planets orbit on the same geometrical plane. In such systems, the companion star can serve as a stabilizer for the planets' orbits, preventing dramatic long-term climate variations that may otherwise be destructive to life as we know it.

These "edge-on" binary systems, because of their alignment, are also excellent candidates for the detection of new planets, according to the researchers: the stars wobble directly toward and away from Earth, creating a signal boost.

For the study, the team identified nearly 600 edge-on binary star systems based on data from the European Space Agency's Gaia DR3 catalog of high-precision stellar astrometry. Drawing from the Gaia dataset, the researchers found the brightest nearby binary star systems, measured their orbits, and simulated the set of expected planets waiting to be discovered orbiting each star.

The result, researchers say, is essentially a prediction for locations in the sky where planet-hunters are more likely to find new planets to identify and characterize—and, for the first time, to compare planets across stars in the same system.

"We outline how this could, for the first time, be used to conduct comparative studies of planet formation where we have a control sample—that is, a second planetary system born together with the first planetary system," Rice said.