The field may protect the Smith Cloud, a gigantic streamer of hydrogen gas, as it plunges into the disk of the galaxy, they said.
Astronomers using radio telescopes to study such clouds say the discovery of the magnetic field could help explain how so-called high velocity clouds, or HVCs, remain mostly intact during mergers with the disks of galaxies, where they would provide fresh fuel for a new generation of stars.
"The Smith Cloud is unique among high-velocity clouds because it is so clearly interacting with and merging with the Milky Way," said Felix J. Lockman, an astronomer at the National Radio Astronomy Observatory in Green Bank, W.Va.
"Its comet-like appearance indicates it's already feeling the Milky Way's influence," he said in an NRAO release Friday.
The Smith Cloud is hurtling toward the Milky Way at more than 150 miles per second and is predicted to impact in approximately 30 million years.
When it does, astronomers believe, it will kick off a spectacular burst of star formation, if it can survive the halo of hot ionized gas surrounding the Milky Way.
"The million-degree upper atmosphere of the Galaxy ought to destroy these hydrogen clouds before they ever reach the disk, where most stars are formed," said Alex Hill, an astronomer at Australia's Commonwealth Scientific and Industrial Research Organization.
"We have long had trouble understanding how HVCs reach the galactic disk," he said. "There's good reason to believe that magnetic fields can prevent their 'burning up' in the halo like a meteorite burning up in Earth's atmosphere."
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