ALMA (ESO/NAOJ/NRAO), C. González

Astronomers have never seen anything like it: two stars, each swaddled in planet-forming discs – and then a third, larger disc around the entire lot. Named IRS 43, the system is 400 light years away from Earth.

The cosmos is chock-full of stars surrounded by planets and planet-forming discs. It’s also home to many binary systems in which each star has its own planetary disc – a rotating disc of gas and dust. We even know of a few planets that orbit both stars in binary systems, though these worlds are rare.

In IRS 43, all three discs are skewed relative to each other, making the system unique in the observed cosmos, says team member Christian Brinch at the University of Copenhagen’s Niels Bohr Institute in Denmark.


Both stars in IRS 43 are very young and about the size of the sun. Each has a disc that is about the size of our solar system, and is probably in the process of forming planets.

The planets can’t be seen directly because they are obscured by dust, but we can trace the regions where they are forming using the Atacama Large Millimeter/submillimeter Array in northern Chile (pictured above).

How the smaller discs formed is an open question, according to Brinch. “All three discs most definitely formed out of the same material. However, whether the two smaller discs formed by fragmenting the big disc or whether they are a result of material flowing in from the big disc is not entirely clear,” he says.

“If the discs were born misaligned, the misalignment would be a result of the formation process itself, and therefore we would expect such systems to be very common. However, if the misalignment is a result of an ejected third star, systems like these would be rather rare.”

A case of misaligned discs Christian Brinch, NBI, KU

The three planetary discs are tumbling around messily, but Brinch says this doesn’t necessarily preclude planets forming. “If they do form planets, I don’t think that it should be a problem to keep it stable,” he says. “One can only try to imagine the incredible day and night cycles these planets will have.”

Journal reference: The Astrophysical Journal Letters, DOI: 10.3847/2041-8205/830/1/L16