From a distance, star-forming cloud L483 appears to be normal. However, as a team of astrophysicists led by Northwestern University zoomed in closer and closer, things became increasingly strange.
As the scientists got closer to the cloud, they noticed that its magnetic field was strangely twisted. Then, as they were inspecting a newborn star within the cloud, they noticed a hidden star tucked behind it.
“It’s basically the star’s sibling,” said Northwestern’s Erin Cox, who led the new study. “We believe that these stars formed far apart and then moved closer together to form a binary. As the star approached its sibling, the dynamics of the cloud shifted, twisting its magnetic field.”
The new findings shed light on binary star formation and how magnetic fields influence the early stages of star formation.
Cox will present his findings at the American Astronomical Society’s (AAS) 240th meeting in Pasadena, California. “The Twisted Magnetic Field of L483” will be presented as part of a session on “Magnetic Fields and Galaxies” on Tuesday, June 14. The study will also be published in the Astrophysical Journal.
Cox works as a postdoctoral fellow at Northwestern University’s Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA).
Stellar nurseries are wondrous and wild places. As dense clouds of gas and dust collapse to form stars, hypersonic outflows of stellar material occur. The magnetic field that surrounds a star-forming cloud is usually parallel to these outflows. Cox and her colleagues discovered this when they observed the large-scale L483 cloud. This typical profile was matched by the magnetic field.
But then the astrophysicists decided to investigate further using NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA), and things got strange. The magnetic field was not, in fact, parallel to the outflows of the newborn stars. The field was instead twisted at a 45-degree angle with respect to the outflows.
“At first, it seemed to match what theory predicted,” Cox said. “If you have a magnetized collapse, the magnetic field governs how the star forms. We anticipate seeing this parallelism. However, theory can say one thing while observations can say another.”
Although more observations are needed, Cox believes the twisted field is caused by a previously hidden sibling star. Using SOFIA, the astrophysics team discovered a newborn star-forming inside a material envelope. Closer inspection with radio telescopes at the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile revealed the second star, which shared the same stellar envelope.
“These stars are still young and forming,” Cox explained. “The stellar envelope is what provides the material for the stars to form. It’s like rolling a snowball around in the snow to make it bigger and bigger. The young stars are ‘rolling’ in material in order to gain mass.”
The two young stars form a binary system about the same distance apart as our sun and Pluto. Astrophysicists currently agree that binaries can form when star-forming clouds are large enough to produce two stars or when the disc rotating around a young star partially collapses to produce a second star.
But, in the case of the twin stars in L483, Cox suspects something unusual is at work.
“There is newer work that suggests it’s possible for two stars to form far apart, and then one star to move in closer to form a binary,” Cox explained. “That’s what we believe is going on here. We don’t know why one star would move toward another, but we believe the moving star shifted the system’s dynamics, causing the magnetic field to twist.”
Cox believes that this new research will eventually provide new insights into the formation of binary stars and the planets that orbit them. The iconic scene from “Star Wars” in which Luke Skywalker wistfully gazes up at the binary stars that orbit his home planet Tatooine is well known to most people. Scientists now 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 simultaneously, and binary stars interact dynamically with each other,” Cox said. “We know planets exist around these double stars from our exoplanet census, but we don’t know much about how these planets differ from those that live around isolated stars. We will be able to test these results with a statistical sample as new instruments for discovering and probing new binary systems become available.”