Is it time for an intervention of galactic proportions? Astronomers say they’ve caught the Milky Way popping pills – giant capsules of gas clouds encapsulated in magnetic fields that are hovering around the fringes of our galaxy. The findings, described in Astrophysical Journal, could help explain how the galaxy has been fueling new star growth.
The Smith Cloud is a cloud of hydrogen gas discovered by and named after Gail Bieger (née Smith) that’s hurtling toward our galaxy at roughly 73 kilometers per second. That's around 163,000 miles per hour. This cloud is huge – weighing the equivalent at least 2 million suns and, if it could be seen with the naked eye, would cover the length of 20 full moons across our sky.
“The Smith Cloud is a laboratory in which to study the behavior of a gaseous cloud as it interacts with the high-altitude galactic [interstellar medium],” the study authors from Australia, the University of Wisconsin and the National Radio Astronomy Observatory wrote.
Scientists say they think that when Smith's Cloud smashes into our galactic plane in something like 27 million years, it’ll trigger a fresh round of star formation.
“The Smith Cloud may be an example of the accretion of gas by the Milky Way that is needed to explain certain persistent anomalies in galactic chemical evolution,” the authors of a previous study in the Astrophysical Journal wrote in 2008.
For this study, scientists trained the Green Bank Telescope in West Virginia and the Wisconsin H-Alpha Mapper Telescope in Arizona on Smith’s and found that the cloud has a weak magnetic field – 50,000 times weaker than Earth’s but still strong enough to keep the high-speed cloud together.
Scientists think that clouds of gas like Smith’s may have been feeding the Milky Way little packets of gas that have fueled new star formation. There's certainly a steady supply: Thousands of these “high velocity clouds” hover around our galaxy’s edges and are swallowed when they occasionally dive into the disk.
But without something to protect the gas clouds as they approach the galactic disk, where star formation can happen, they’d disintegrate in the warm outer halo before reaching the disk, where they could fuel stellar growth.
The magnetic field, they believe, keeps the gas cloud together until it lands in the disk and then can be properly digested, the authors said.
These gas clouds are fascinating in their own right, probably a mix of gas from small galaxies getting eaten by our much larger Milky Way and primordial gas from the universe’s early days that never made it into a star. But understanding how Smith's cloud works could help scientists understand how such celestial bodies move and interact with their surroundings, the authors said.
“The presence of the magnetic field may contribute to the survival of high velocity clouds like the Smith Cloud as they move from the galactic halo to the disk. We expect these data to provide a test for magnetohydrodynamic simulations of infalling gas,” the study authors wrote.