61,563 research outputs found
Star Formation at the Galactic Center
Molecular clouds at the Galactic center (GC) have environments considerably
different from their disk counterparts. The GC may therefore provide important
clues about how the environment affects star formation. Interestingly, while
the inner 50 parsecs of our Galaxy include a remarkable population of high-mass
stars, the initial mass function (IMF) appears to be consistent with a Salpeter
slope down to ~ 1 solar mass. We show here that the loss of turbulent pressure
due to ambipolar diffusion and the damping of Alfven and fast MHD waves can
lead to the formation of dense condensations exceeding their Jeans limit. The
fragmentation and subsequent collapse of these condensations is similar to the
diffusion-driven protostellar collapse mechanism expected to occur within
nearby "regular" molecular clouds. As such, a Salpeter IMF at the GC is not
surprising, though the short dynamical timescales associated with the GC
molecular clouds may help explain the lower star formation efficiency observed
from this region.Comment: Accepted for publication in PAS
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
The influence of star clusters on galactic disks: new insights on star-formation in galaxies
Stars form in embedded star clusters which play a key role in determining the
properties of a galaxy's stellar population. Physical mechanisms discussed in
this paper are runaway stars shot out from young clusters, binary-star
disruption in clusters, gas blow-out from clusters and the origin of thick
galactic disks. I emphasise that the SNIa rate per low-mass star depends on the
star-clusters formed in a galaxy and I discuss the IGIMF theory. Based on the
IGIMF theory, the re-calibrated Halpha-luminosity--SFR relation implies dwarf
irregular galaxies to have the same gas-depletion time-scale as major disk
galaxies, suggesting a major change in our understanding of dwarf-galaxy
evolution. The IGIMF-theory also naturally leads to the observed radial Halpha
cutoff in disk galaxies without a radial star-formation cutoff. It emerges that
the thorough understanding of the physics and distribution of star clusters may
be leading to a major paradigm shift in our understanding of galaxy evolution.Comment: 12 papges, to appear in The Galactic disk in a cosmological context,
IAUS254, eds J. Andersen, J. Bland-Hawthorn and B. Nordstro
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