From a magnified distant view, the star-forming cloud L483 appears normal. But when a team of astrophysicists led by Northwestern University got closer and closer, things got stranger and stranger.
As the researchers looked closer into the cloud, they noticed that its magnetic field was oddly twisted. And then – as they examined a newborn star in the cloud – they spotted a hidden star, nestled behind it.
“He’s the star’s brother, basically,” said Erin Cox of Northwestern, 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 sibling, it 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 will present this research at the 240th meeting of the American Astronomical Society (AAS) in Pasadena, California. “The twisted magnetic field of L483” will take place on Tuesday, June 14, as part of a session on “Magnetic fields and galaxies”. The Astrophysical Journal will also publish the study next week.
Cox is a postdoctoral associate at the Center for Interdisciplinary Astrophysics Exploration and Research (CIERA) at Northwestern.
Stellar nurseries are wild and wondrous places. When dense clouds of gas and dust collapse to form stars, they launch outflows 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 observed the L483 cloud on a large scale, they discovered this. 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 when things got weird. The magnetic field was not in fact parallel to the outflows of the nascent stars. Instead, the field was twisted at a 45 degree angle to the flows.
“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 expect to see this parallelism. But theory may say one thing, and observations may say another.”
Unusual binary formation
Although more observations are needed, Cox believes a previously hidden sister star may be responsible for the twisted field. Using SOFIA, the astrophysics team spotted a newborn star forming inside an envelope of matter. But after closer examination with radio telescopes at the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, the researchers spotted 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 through the snow to make it bigger and bigger. Young stars “roll” through the material to accumulate the mass.”
At roughly the same distance between our sun and Pluto, the two young stars form a binary system. Currently, astrophysicists agree that binaries can form when star-forming clouds are large enough to produce two stars or when the disk revolving 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 that it’s possible for two stars to form far apart and then one star to approach to form a binary,” Cox said. “We think that’s what’s happening here. We don’t know why one star would move 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 wistfully at the binary stars around which his home planet, Tatooine, revolves. Now, scientists know that this scenario isn’t just science fiction; planets orbiting binary stars could potentially be habitable worlds.
“Learning how binary stars form is exciting because planet and star formation occur at the same time, and binary stars dynamically interact with each other,” Cox said. “In our census of exoplanets, we know that planets exist around these double stars, but we don’t know much about how these planets differ from those living around single stars. With the release of new instruments to discover and probe new binary systems, we will be able to test these results with a statistical sample.”
The study, “The twisted magnetic field of protobinary L483,” was supported by NASA and the National Science Foundation.
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