Huge hydrogen clouds that measure 100-light-years across hover in the void between the Milky Way galaxy and intergalactic space, according to a new report. Previous research had revealed the presence of hydrogen gas floating above the plane of our galaxy. But where it came from or how it was distributed remained unclear due to instrument limitations. Now observations using the Robert C. Byrd Green Bank Telescope (GBT) have exposed the shape of the neutral hydrogen masses. "These objects were just below the ability of the older telescopes to detect," says F. Jay Lockman of the National Radio Astronomy Observatory, "but I looked with the GBT, and they popped right out."

In a paper accepted for publication in Astrophysical Journal Letters, Lockman reports that the group of clouds is located toward the center of the Milky Way, 15,000 light-years from the earth, and that each cloud contains between 50 and 100 solar masses of hydrogen. (The image shows an artist's conception of the Milky Way with an insert of GBT data.) He further notes that the clouds, which float about 5,000 light-years above the plane of our galaxy, are coupled to the Milky Way's movements. That is, as the galaxy spins, so do the clouds--an indication, Lockman says, that "these are home grown objects, and not interlopers from outside our own galaxy." One potential source is supernova explosions that continuously feed superheated hydrogen gas into the Milky Way's halo, which subsequently cools to form the clouds. Further radio telescope observations are underway to gather more information about the intricacies of the hydrogen clouds, including their inner structure.

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