Nicholas Hunt-Walker
City University of New York - York College

REU program-Summer 2009
Research projects of other REU students
Univ. of Wisconsin - Madison
Madison, WI 53706

Email: nhuntwalker [at] gmail [dot] com

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Background Information


What should we know about dwarf spheroidal galaxies?

Dwarf spheroidal galaxies are special in that they possess low luminosities, an old stellar population, large separations between luminous objects, and are virtually devoid of gas and dust. Those last two points are what makes dwarf spheroidal galaxies such great environments for X-ray studies. Because there's almost no intervening matter, and because the objects are spaced far enough apart, the X-rays don't get absorbed and reradiated at longer wavelengths, and the sources of these rays are readily distinguishable. Thus, whatever extreme events happen in or beyond dwarf galaxies are seen directly by our X-ray observatory.

Sculptor Dwarf Spheroidal Galaxy

The old stellar population is especially crucial in X-ray binary studies, as one requires an evolved stellar population in order to even have compact objects, such as white dwarfs, neutron stars, or black holes. As such, population ages in dwarf galaxies have been shown to be, on average, older than 2.5 Gyr.

Dwarf spheroidal galaxies also contain a large amount of dark matter. This has been inferred from studies that have shown that the mass derived from the motions of stars within the galaxies are much larger than what can be accounted for by the luminous matter in the galaxy. Thus, cosmologists turn to the dark matter hypothesis.

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