Check out a 3D view of binary star-planet system — the first of its kind

This new data could help scientists better understand the formation of planets.
Fabienne Lang
Binary star system
Binary star system

Sophia Dagnello, NRAO/AUI/NSF 

Thanks to an almost imperceptibly small wobble of a star, astronomers were able to discover a Jupiter-like planet orbiting that star – and even better than that, there were, in fact, two stars.

This starry binary pair was discovered using the National Science Foundation’s Very Long Baseline Array (VLBA), which produced the first-ever determination of the complete, 3D structure of the orbits of a binary pair of stars and a planet orbiting one of them.

Not only is this a mesmerizing achievement, the astronomers said in a statement, but it can also provide valuable new insights into the planet formation process.

The team published its detailed findings in The Astronomical Journal.

Why is this discovery significant?

So far, over 5,000 extrasolar planets have been discovered. However, only three of those were discovered using the same technique – astrometry– used to find this binary star-planet system.

That said, the feat of determining the 3D architecture of a binary-star system that includes a planet “cannot be achieved with other exoplanet discovery methods,” said Salvador Curiel, of the National Autonomous University of Mexico (UNAM).

The two stars in question, which are called GJ 896AB, are about 20 light-years from Earth, making them close neighbors of ours by astronomical standards. They're red dwarf stars, the most common kind in our Milky Way galaxy, and the larger one, around which the planet orbits, has about 44 percent of the mass of our Sun, while the smaller is about 17 percent as massive as the Sun. They are separated by about the distance of Neptune from the Sun, and orbit each other once every 229 years, explains the press release.

Check out a 3D view of binary star-planet system — the first of its kind
In this artist's conception, a small star (orange) is orbited by a Jupiter-like planet (blue), and by a more-distant companion star (red).

The astronomers took data from optical observations of the system made between 1941 and 2017 – a fair amount of time. They also used data from VLBA observations between 2006 and 2011.

Thanks to VLBA's attuned ability to see in fine detail, something called the supersharp resolution, the astronomers produced extremely precise measurements of the stars’ positions over time. The astronomers could carry out extensive analysis of the data that ultimately revealed the stars’ orbital motions and their common motion through space.

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From there, the team was able to trace the bigger star's motion, which showed a slight wobble, which ultimately revealed the existence of the planet. The wobble is caused by the planet's gravitational pull on the star.

The astronomers were able to calculate that the planet has roughly twice the mass of Jupiter and orbits the star every 284 Earth days. It sits at a distance a little less than Venus’ distance from the Sun. The planet’s orbit is inclined roughly 148 degrees from the orbits of the two stars.

Gisela Ortiz-León, UNAM and the Max Planck Institute for Radioastronomy, said, "This is the first time that such dynamical structure has been observed in a planet associated with a compact binary system that presumably was formed in the same protoplanetary disk."

In terms of what this means for us and our understanding of planetary systems, astronomers believe this astrometric technique will be a valuable tool for characterizing even more planetary systems.

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