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Galactic Bridge

March 15, 2010

You can't walk across it, but there's a bridge between our own Milky Way galaxy and two of its companions -- a bridge of hydrogen gas. Known as the Magellanic Stream, it's more than 200,000 light-years long.

The stream comes from the Large and Small Magellanic Clouds -- two fairly small galaxies that appear to be orbiting the Milky Way. The stream was discovered decades ago. And a recent study by astronomers at the University of Virginia has filled in some holes.

Earlier studies indicated that there were gaps in the stream. But the Virginia astronomers found that the stream is unbroken from the Magellanic Clouds all the way to the Milky Way. They filled in the gaps by staring at that region of space for a total of about four days with the giant Green Bank radio telescope in West Virginia, then adding observations made with other telescopes.

The astronomers suggest that the stream was born when the two small galaxies passed quite close to each other about two and a half billion years ago. The encounter caused big clouds of gas and dust in each galaxy to ram together and give birth to new stars.

The hottest and heaviest of these stars produced powerful "winds" that blew gas away from the small galaxies. These stars later exploded as supernovae, adding more energy to the stream. The Milky Way's strong gravity pulled on the stream of gas, creating the bridge that exists today -- a bridge between galaxies.

Script by Damond Benningfield, Copyright 2010

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