Astronomers Map Chaotic Galaxy's Magnetic Field

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Considering its tumultuous nature, the Large Magellanic Cloud (LMC) exhibits a surprisingly ordered magnetic field, astronomers have discovered. The observations, detailed today in the journal Science, have resulted in the most detailed map yet of another galaxy's magnetism and provide a starting point for determining the magnetism of most of the local universe.

The LMC is the Milky Way galaxy's closest neighbor and, as a result, feels the effects of our galaxy's gravity. In addition, the LMC has experienced a variety of violent events, such as star formation and supernova explosions, which should disrupt a surrounding magnetic field. Scientists thus expected the magnetic field of the LMC to show signs of perturbation. Instead, they were surprised to find the field orderly and smooth. "It's like having a birthday party all afternoon for a bunch of four-year-olds and then finding the house still neat and tidy when they leave," remarks study leader Bryan Gaensler of the Harvard-Smithsonian Center for Astrophysics. "Some powerful forces must be at work to keep the magnetic field from being messed up."

The team measured the LMC's magnetic field by observing how it affected radio emissions from background sources as they passed through it, a technique previously used on only two other galaxies, the Milky Way and one called M31. As to what is keeping LMC's field in order, a number of theories exist. The current front-runner, according to the researchers, is a process driven called a cosmic-ray driven dynamo, which requires vigorous star formation. Says Gaensler: "You could say this galaxy is thriving on chaos."

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