Black Holes vs. Dark Matter

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Dr Gebhardt and his team will use a fiber-fed spectrograph at the McDonald 2.7-meter telescope to measure stellar motions in the outer parts of nearby elliptical galaxies. The large fibers will gather diffuse light over a 2-arcminute field of view, which reaches the outskirts of the target galaxy. These observations will be combined with detailed measurements in the central regions with the Hubble Space Telescope and with 10-meter ground-based telescopes using adaptive optics. The measured motions will be compared with both axisymmetric and triaxial orbit-based models, to place limits jointly on the distribution of dark matter and the mass of a central black hole. This team has already shown that these two quantities are difficult to measure independently, and that omitting the dark halo from models of the central galaxy yields too small a mass for the black hole. The team will concentrate on galaxies for which other mass measures, such as those from X-ray-emitting gas, or the motions of planetary nebulae or globular star clusters, are available for comparison. The computationally expensive modeling will be done at the Texas Advanced Computing Center. This award will support postdoctoral scholar Shen, a graduate student, and undergraduate researchers. As part of his NSF CAREER award AST-0349095, Dr Gebhardt built a web page, available both in English and in Spanish, to make his black hole research accessible to the public. He will maintain and develop this website, in association with StarDate magazine and the McDonald Observatory's visitor center.