Classical or Modified Newtonian Dynamics? Testing MOND in Palomar 14
Abstract
The dark matter paradigm and cold dark matter (CDM) cosmology are widely accepted theories on which much of our understanding of the properties and evolution of the Universe is based. Yet these paradigms face a number of serious problems (e.g., the substructure crisis). A heuristic alternative to dark matter is the theory of modified Newtonian dynamics (MOND) and its relativistic formulation. For more than 20 years, MOND has successfully defied all attempts to disprove it. A few years ago we showed that for distant outer halo globular clusters, the expected line-of-sight velocity dispersions in the case of MOND exceed those expected in the case of Newtonian gravity by up to a factor of three (Baumgardt, Grebel, & Kroupa 2005). Such a large difference should be observationally measurable, and determining these dispersions provides a stringent test for MOND. We hence observed the outer halo globular cluster Palomar 14 with the Very Large Telescope at the European Southern Observatory in order to measure its line-of-sight velocity dispersion. We find a very low velocity dispersion, consistent with the Newtonian value and significantly below the prediction of MOND. This would seem to be a conclusive verdict against MOND; however, MOND might still be able to account for this low dispersion if the stellar mass function of Palomar 14 is significantly depleted in low-mass stars. We are thus also measuring the cluster's luminosity function to obtain a lower limit on its mass and to decide on the validity of MOND.
- Publication:
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American Astronomical Society Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AAS...211.5801J