I consider the physics of gravitational instabilities in the presence of dynamically important radiation pressure and gray radiative diffusion, governed by a constant opacity κ. For any non-zero radiation diffusion rate on an optically-thick scale k−1, the medium is unstable unless the classical gas-only isothermal Jeans criterion is satisfied. If the radiation acoustic sound crossing timescale...

Using hydrodynamic simulations we investigate the time evolution and fragmentation of regions within molecular clouds which have lost their turbulent support leading to gravitational contraction. The initial density distributions are described by random Gaussian fluctuations with varying slopes ν of the power spectrum P (k) ∝ k , covering the range from flat (ν = 0) to very steep spectra (ν = 3...

A generalized form of Wien’s displacement law and the blackbody radiation laws of (a) Rayleigh and Jeans, (b) Rayleigh, (c) Wien and Paschen, (d) Thiesen and (e) Planck are derived using principles of dimensional analysis. This kind of scaling is expressed in a strictly mathematical manner employing dimensional π-invariants analysis sometimes called Buckingham’s π-theorem. It is shown that in t...

We study the properties of density perturbations of a two-component plasma with a temperature difference on a homogeneous and isotropic background. For this purpose we extend the general relativistic gauge invariant covariant (GIC) perturbation theory to include a multi-fluid with a particular equations of state (ideal gas) and imperfect fluid terms due to the relative energy flux between the t...

We present spectroscopy and imaging with the Very Large Telescope (VLT) of the isolated neutron star RX J1856.5−3754. Little is known about the nature of this source other than that it is a nearby hot neutron star. Our VLT spectrum does not show any strong emission or absorption features. With considerable care to photometric calibration, we obtain photometric measurements over the optical and ...

The formation of globular clusters and their relation to the distribution dark matter have long puzzled astronomers. One most recently-proposed cluster channels ties ancient star large-scale streaming velocity baryons relative in early Universe. These velocities affect global infall into halos, high-redshift halo mass function, earliest generations stars. In some cases, may result dense regions...