Dwarf Galaxies Caught Speeding

Milky Way Revised

The Large Magellanic Cloud, a satellite galaxy of the Milky Way. Picture taken by Hubble (Wikimedia Commons)
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Nitya Kallivayalil didn’t set out to change the way we think about our corner of the universe. But the 27-year-old doctoral student at the Harvard-Smithsonian Center for Astrophysics may have done just that. By comparing images taken two years apart with NASA’s Hubble Space Telescope, Kallivayalil, her adviser Charles Alcock and astronomer Roeland van der Marel found that two neighboring dwarf galaxies called the Magellanic Clouds are moving almost twice as fast as was previously thought. “I was very surprised,” says Kallivayalil.

Astronomers have long believed that the Magellanic Clouds orbit our own, more massive galaxy, the Milky Way. But it seems the dwarf galaxies are moving so quickly that they may be zooming through our intergalactic neighborhood, destined to streak by in the next few billion years. Alternatively, if the clouds are indeed satellite galaxies, the Milky Way itself must have much more mass than is currently estimated—the extra would be needed to hold the clouds gravitationally—or it must have an irregular distribution of the dark matter that makes up most of its mass.

Either way, says Alcock, director of the Harvard-Smithsonian Center for Astrophysics, Kallivayalil’s finding “adds an unexpected new perspective to the dynamics of the Milky Way galaxy.”


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