This composite image shows the huge extent of a spiral galaxy’s magnetic field. Galaxy NGC 4217 is a star-formingspiral galaxy similar to the Milky Way. It is about 67 million light-years from Earth in the constellation Ursa Major, according to astronomers in an international collaboration called CHANGES. The galaxy is seen edge-on in a visible-light image from the Sloan Digital Sky Survey and Kitt Peak National Observatory. The magnetic field lines, in green, are revealed by Karl G. Jansky at the Very Large Array (VLA) radio telescope of the National Radio Astronomy Observatory, which is supported by the National Science Foundation.
Professor Daniel Wang in the astronomy department is a co-author of a paper released with this image July 21. He says the work “demonstrates that the magnetic field around galaxies plays an essential role in regulating their life.”
He and colleagues say NGC 4217’s magnetic field lines extend as much as 22,500 light-years beyond the galaxy disk. Scientists know that magnetic fields play an important role in many processes such as star formation in galaxies. However, it is not fully understood how such huge magnetic fields are generated and maintained. A leading explanation, called the dynamo theory, suggests that magnetic fields are generated by plasma motion within the galaxy disk. Ideas about the cause of the kinds of large vertical extensions seen in this image are more speculative, and astronomers hope that further observations and more analysis will answer some of the outstanding questions.