Back in the Empire

StarDate: January 15, 2009

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Our home galaxy, the Milky Way, is a galactic giant that rules an empire of lesser galaxies -- at least 20 of them. These smaller puffs of stars and gas are "satellites" that revolve around the Milky Way just like the Moon orbits Earth.

Recently, though, observations by Hubble Space Telescope indicated that one of the satellite galaxies wasn't really a satellite at all. It seemed to be moving much faster than had been thought -- so fast that the Milky Way's gravity couldn't hold on to it. This wayward galaxy was no ordinary satellite: it was the Large Magellanic Cloud, by far the Milky Way's brightest and most massive companion.

But the Milky Way seems to have struck back. Astronomers at the Harvard-Smithsonian Center for Astrophysics recently reported that the Milky Way is about 50 percent more massive than had been thought. If so, then its gravity is stronger, too. What's more, the Magellanic Cloud seems to be moving a bit more slowly than the Hubble observations had implied.

When the astronomers worked out the numbers, they found that the Large Magellanic Cloud is indeed bound to the Milky Way. It orbits the Milky Way once every six billion years, and attains a maximum distance of more than a million light-years.

Right now, it's at it's closest to the Milky Way -- just 160,000 light-years away from Earth. That makes it one of our closest galactic neighbors -- a massive colony just beyond the Milky Way.

Script by Ken Croswell, Copyright 2008

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