We define three requirements for accurate simulations that attempt to model circumstellar disks and the formation of collapsed objects (e.g. planets) within them. First, we define a resolution requirement based on the wavelength for neutral stability of self gravitating waves in the disk, where a Jeans analysis does not apply. For particle based or grid based simulations, this criterion takes t...

Prieto and Docobo's approach to the two-body problem with isotropic mass loss is used to study the dynamical evolution of the orbital elements of the binaries γ Persei and α Centauri under the assumption that mass losses obey the Eddington-Jeans law, with separate parameters for each component of the binaries.

We note that current observational evidence strongly favors a conventional recombination of ionized matter subsequent to redshift z = 1200, followed by reionization prior to redshift z = 5 and compute how this would have occurred in a standard scenario for the growth of structure. Extending prior semi-analytic work, we show by direct, high-resolution numerical simulations (of a COBE normalized ...

The molecular component of the Galaxy is comprised of turbulent, magnetized clouds, many of which are self-gravitating and form stars. To develop an understanding of how these clouds’ kinetic and structural evolution may depend on their level of turbulence, mean magnetization, and degree of self-gravity, we perform a survey of direct numerical MHD simulations in which three parameters are indep...

The isothermal gravitational collapse and fragmentation of a molecular cloud region and the subsequent formation of a protostellar cluster is investigated numerically. The clump mass spectrum which forms during the fragmentation phase can be well approximated by a power law distribution dN/dM ∝ M. In contrast, the mass spectrum of protostellar cores that form in the centers of Jeans unstable cl...

We study the generation of magnetosonic waves in galactic gaseous discs taking account of the magnetic field, differential rotation and self-gravity. The special case of perturbations is considered with the wavevector perpendicular to the magnetic field. The necessary condition of the amplification of seed perturbations is the presence of differential rotation and nonvanishing radial component ...

We have constructed axisymmetric dynamical models of the edge-on S0 galaxy NGC 4342: simple two-integral Jeans models as well as fully general, three-integral models using a modified version of Schwarz-schild's orbit superposition technique. The two-integral models suggest a black hole (BH) of 3 or 6 × 10 8 M ⊙ , depending on the data set. The three-integral models can fit all ground-based and ...

Our second resembles it slightly. Newton, Jeans, and Planck have used "God" to account for things they could not explain. Biologists, ignorant of mechanisms underlying functions, have introduced "Nature," "Vital Force," "Nervous Energy," "the Unconscious," or some other pseudonym for God. Each of these supposititious explanations, to quote Sir Thomas Browne, "puts the honest Father to the refug...

We use the public release of ≃ 100, 000 galaxies of the Two Degree Field Galaxy Redshift Survey (2dFGRS) to analyze the internal dynamics of galaxy clusters. We select 43 non-interacting clusters which are adequately sampled in the 2dFGRS public release. Members of these clusters are selected out to ∼ 2 virial radii. We build an ensemble cluster by stacking together the 43 clusters, after appro...

We search for evidence of dark matter in the Milky Way by utilizing the stellar number density distribution and kinematics measured by the Sloan Digital Sky Survey (SDSS) to heliocentric distances exceeding ∼10 kpc. We employ the cylindrically symmetric form of Jeans equations and focus on the morphology of the resulting acceleration maps, rather than the normalization of the total mass as done...