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Hydrogen Distribution in Whirlpool Galaxy
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Hydrogen Distribution in Whirlpool Galaxy

May 30, 2011
The distribution of HI hydrogen in the Whirlpool Galaxy (M51)--as determined by THINGS (The HI Nearby Galaxy Survey), a survey conducted by the Very Large Array (VLA)--extends far beyond the visible stars in the galaxy and its satellite NGC 5195 (marked by cross), which is situated in the short arm of the spiral. Analysis of perturbations in the hydrogen distribution can be used to predict the location of such satellites, in particular, those satellites that are composed primarily of dark matter and are thus too faint to be detected easily. The VLA is part of the National Science Foundation (NSF)-supported National Radio Astronomy Observatory.

Many large galaxies, like the Milky Way, are thought to have satellite galaxies that are too dim to see because they are dominated by "dark matter." Sukanya Chakrabarti, a postdoctoral fellow and theoretical astronomer at the University of California, Berkeley, has developed a mathematical method to find "dark" satellite galaxies by analyzing the ripples in the hydrogen gas distribution in spiral galaxies. Collaborating with other researchers, some of who are funded by NSF, Chakrabarti looked at data for the Whirlpool Galaxy, which has a companion galaxy one-third its size, and NGC 1512, a barred spiral galaxy with a satellite one-hundredth its size. Her mathematical analysis correctly predicted the mass and location of these satellites.

"This approach has broad implications for many fields of physics and astronomy--for the indirect detection of dark matter as well as dark-matter-dominated dwarf galaxies, planetary dynamics and for galaxy evolution driven by satellite impacts," she said. To learn more, see the UC-Berkeley news story "Forget Planet X! New technique could pinpoint Galaxy X."