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An Extreme Dark Matter Dominated Galaxy

6 Dec 2015, 22:00 UTC
An Extreme Dark Matter Dominated Galaxy
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A cluster of stars can be considered a galaxy if it shows evidence for dark matter, where the stars in the cluster are moving too fast for the gravitational field from just the stars alone to hold the cluster together. Additionally, a cluster of stars can also be considered a galaxy if the stars exhibit different metallicities (i.e. different abundances of elements heavier than hydrogen and helium), which indicates multiple episodes of star formation. Dwarf galaxies tend to contain very few stars but a lot of dark matter. Triangulum II is a dwarf galaxy located just beyond the edge of the Milky Way. It contains only ~1000 stars and it is a satellite galaxy of the Milky Way.By observing the motion of six stars in Triangulum II, the gravitational force acting on the stars can be measured. This technique allows the mass of the galaxy to be estimated. The total mass of Triangulum II is found to be much greater than the mass of all its stars. Although the galaxy contains ~2 million times the Sun’s mass, its total luminosity is only ~450 times the Sun’s luminosity. In fact, Triangulum II has one of the largest mass-to-light ratios of any ...

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