A Test to See in the Dark

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Science  09 Dec 2011:
Vol. 334, Issue 6061, pp. 1324
DOI: 10.1126/science.334.6061.1324-a

According to current models of structure formation in the universe, large galaxies, like our Milky Way, formed from the merging of many smaller systems. The models predict that a large number of small satellite galaxies should exist in our galaxy's vicinity, but this prediction does not match the observations. However, some of these small galaxies may be too difficult to detect, because they may be dominated by dark matter, a mysterious type of matter that does not emit or absorb light but does exert a gravitational pull. The Tidal Analysis method, developed to derive the locations and masses of satellite galaxies from the gravitational perturbations the satellites induce in the gas disk of the primary galaxy, has the potential to reveal satellite galaxies dominated by or composed entirely of dark matter. To demonstrate its validity, Chakrabarti et al. applied the Tidal Analysis method to two nearby spiral galaxies, M51 and NGC 1512, which each interact with a known visible companion. The method successfully recovered the masses and locations of the smaller companions; their masses ranging from one-third to one-hundredth of the mass of the primary galaxy.

Astrophys. J. 743, 35 (2011).

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