Traveling stars can form binary systems


A cosmic event captured with the SOFIA airborne observatory and the ALMA radio telescope provided new proof that traveling stars can form binary systems.

From a distance, the star-forming cloud L483 appears normal. But as a team of astrophysicists led by Northwestern University got closer and closer, things got stranger and stranger.

When the researchers took a closer look at the cloud, they noticed that its magnetic field was oddly twisted. And then, as they examined a newborn star in the cloud, they saw a hidden star, hidden behind her.

“He’s the star’s brother, basically,” he said. it’s a statement Erin Cox is a postdoctoral associate at Northwestern’s Center for Interdisciplinary Research and Exploration in Astrophysics (CIERA), who led the new study. “We think these stars formed very far apart and one moved closer to the other to form a binary. As the star moved closer to its sister, changed the dynamics of the cloud to twist its magnetic field.”

The new findings provide insight into how binary stars form and how magnetic fields influence the early stages of star development.

Cox is presenting this research at the 240th meeting of the American Astronomical Society (AAS) in Pasadena, California. The Astrophysical Journal will also publish the study.

Stellar nurseries are wild and wondrous places. When dense clouds of gas and dust collapse to form stars, they launch streams of stellar matter at hypersonic speeds. A magnetic field surrounding a star-forming cloud is generally parallel to these outflows. When Cox and his collaborators looked at the large-scale L483 cloud, they found exactly that. The magnetic field corresponded to this typical profile.

But then astrophysicists decided to take a closer look with NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA), and that’s where things got weird. The magnetic field was not in fact parallel to the outflows of the nascent stars. Instead, the scope was twisted at a 45 degree angle to the exits.

“At first it was consistent with what the theory predicts,” Cox said. “If you have a magnetized collapse, then the magnetic field controls star formation. We hope to see that parallel. But theory can say one thing and observations can say another.

Although more observations are needed, Cox believes a previously hidden sister star may be responsible for the twisted field. Using SOFIA, the astrophysics team detected a newborn star forming inside an envelope of matter. But after closer examination with radio telescopes on the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, the researchers detected the second star, sharing the same stellar envelope.

“These stars are still young and in formation,” Cox said. “The stellar envelope is what provides the material to form stars. It’s like rolling a snowball over the snow to make it bigger and bigger. Young stars are ‘rolling’ in hardware to pack on mass.”

At roughly the same distance between our sun and Pluto, the two young stars form a binary system. Astrophysicists now agree that binaries can form when star-forming clouds are large enough to produce two stars or when the disk around a young star partially collapses to form a second star.

But for the twin stars of L483, Cox suspects something unusual is at play.

“More recent work suggests it’s possible for two stars to form far apart and then one star to come closer to form a binary,” Cox said. “We think that’s what’s happening here. We don’t know why one star is moving towards another, but we think the moving star changed the dynamics of the system to twist the magnetic field“.

Cox thinks this new work could ultimately provide new insights into how binary stars and the planets that orbit them form. Most people are familiar with the iconic scene from “Star Wars,” in which Luke Skywalker gazes longingly at the binary stars orbiting his home planet, Tatooine. Scientists now know that this scenario is not just science fiction; planets orbiting binary stars could potentially be habitable worlds.

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