19,780 research outputs found
All The Things I Can\u27t Throw Away
In lieu of an abstract, below is the essay\u27s first paragraph.
Taking after my mother now, I save receipts in the center billfold of my wallet. Loose change, half empty tubes of lipstick, gum wrappers. Postcards, photographs in albums, birthday cards, yearbooks signed by forgotten friends
Baryons and Their Halos
Galaxies are composed of baryonic stars and gas embedded in dark matter
halos. Here I briefly review two aspects of the connection between baryons and
their halos. (1) The observed baryon content of galaxies falls short of the
cosmic baryon fraction by an amount that varies systematically with mass. Where
these missing baryons now reside is unclear. (2) The characteristic
acceleration in disk galaxies correlates strongly with their baryonic mass
surface density. This implies a close coupling between the gravitational
dynamics, which is presumably dominated by dark matter, and the purely baryonic
components of galaxies.Comment: 4 pages. Invited contribution to "Hunting for the Dark: The Hidden
Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P. Debattista &
C.C. Popescu, AIP Conf. Ser., in pres
Some Systematic Properties of Rotation Curves
The rotation curves of spiral galaxies obey strong scaling relations. These
include the Tully-Fisher and baryonic Tully-Fisher relations, and the mass
discrepancy--acceleration relation. These relations can be used to place
constraints on the mass-to-light ratios of stars. Once the stellar mass is
constrained, the distribution of dark matter follows. The shape of the dark
matter distribution is consistent with the expectations of NFW halos exterior
to 1 kpc, but the amplitude is wrong. This is presumably related to the
long-standing problem of the normalization of the Tully-Fisher relation and may
imply a downturn in the amplitude of the power spectrum at small scales. More
fundamentally, the persistent success of MOND remains a troubling fact.Comment: 8 pages including 7 figures. Invited review for the 21st IAP
Colloquium: Mass Profiles and Shapes of Cosmological Structures, eds. G. A.
Mamon, F. Combes, C. Deffayet, B. For
Predictions and Outcomes for the Dynamics of Rotating Galaxies
A review is given of a priori predictions made for the dynamics of rotating
galaxies. One theory - MOND - has had many predictions corroborated by
subsequent observations. While it is sometimes possible to offer post hoc
explanations for these observations in terms of dark matter, it is seldom
possible to use dark matter to predict the same phenomena.Comment: 36 pages (10 are references), 9 figures. Invited review for the
Galaxies special Issue "Debate on the Physics of Galactic Rotation and the
Existence of Dark Matter." Provides test cases for the importance of prior
predictions in the application of the scientific metho
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