In The Field

AAS: Big gas cloud headed our way

First it’s rogue black holes on the loose, now it’s giant gas clouds speeding toward the Milky Way. Astronomers have identified a big glob of hydrogen that’s zooming towards us at more than 150 miles per second – and will hit our galaxy 20 million to 40 million years from now.


Scientists have known about the cloud since 1963, when astronomer Gail Smith identified it before dropping out of research. At the time, no one knew whether the cloud was headed for us, away from us, or something in between.

New observations from the Green Bank radiotelescope – the big dish in the West Virginia mountains that’s surrounded by a zone of cellphone silence, so as not to interfere with the telescope – have pinned down the cloud’s trajectory.

“I’ve been going around calling it the most interesting hydrogen cloud in the known universe,” says Jay Lockman, an astronomer at the National Radio Astronomy Observatory who is also known for his banjo-playing skills. Lockman and his colleagues looked at the cloud nearly 40,000 times with the Green Bank telescope and put together a detailed three-dimensional picture of it.

Right now Smith’s Cloud is about 40,000 light-years from Earth. But when it gets here, it is likely to slam into one of the spiral arms of the Milky Way – fortunately a couple of arms over from the one in which the sun, and you, reside. The collision will probably trigger a burst of star formation – lighting up the local sky in true celestial fireworks.

Lockman said that he was able to reach Gail Smith by telephone just within the past week, to let her know that her discovery of decades ago was literally about to come home. For pictures of where exactly it will hit, check out the NRAO’s press release here.


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