124 research outputs found
MOND and the seven dwarfs
Gerhard had recently analyzed the data on seven dwarf spheroidals, and
concluded that these disagree with the predictions of MOND. We contend that
this conclusion is anything but correct. With new data for three of the dwarfs
the observations of all dwarfs are in compelling agreement with the predictions
of MOND. Gerhard found MOND M/L values that fall around a few solar units, as
expected if MOND is a valid alternative to dark matter. His sole cause for
complaint was that some of his MOND M/L values were still outside the range of
``reasonable'' stellar values. This, we say, was easily attributable to
uncertainties in the data, such as in the velocity dispersions, luminosities,
core radii, etc., and in the assumptions that underlie the analysis, such as
isotropic velocity distribution, light-distribution fits, etc.. There are now
new, much improved determinations of the velocity dispersions for three of the
dwarfs, in particular for the two dwarfs for which Gerhard found high MOND M/L
values. In fact, within just the quoted errors on the velocity dispersions and
the luminosities, the MOND M/L values for all seven dwarfs are now perfectly
consistent with stellar values, with no need for dark matter.Comment: 10 pages; Latex; requires aaspp.sty, attached at the end
New Physics at Low Accelerations (MOND): an Alternative to Dark Matter
I describe the MOND paradigm, which posits a departure from standard physics
below a certain acceleration scale. This acceleration as deduced from the
dynamics in galaxies is found mysteriously to agree with the cosmic
acceleration scales defined by the present day expansion rate and by the
density of `dark energy'. I put special emphasis on phenomenology and on
critical comparison with the competing paradigm based on classical dynamics
plus cold dark matter. I also describe briefly nonrelativistic and relativistic
MOND theories.Comment: 15 pages, minor coorrections. proceedings of: "The Invisible Universe
International Conference", Paris, June 2009 (J.M. Alimi et al. eds.
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