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We consider the stability properties of the ocean of accreting magnetic neutron stars. It turns out that the ocean is always unstable due to the combined influence of the temperature and chemical composition gradients along the surface and…
We review current understanding of star formation, outlining an overall theoretical framework and the observations that motivate it. A conception of star formation has emerged in which turbulence plays a dual role, both creating…
The fundamental difference between accretion around black holes and neutron stars is the inner boundary condition, which affects the behavior of matter very close to the compact objects. This leads to formation of additional shocks and…
Dust waves and bow waves result from the action of a star's radiation pressure on a stream of dusty plasma that flows past it. They are an alternative mechanism to hydrodynamic bow shocks for explaining the curved arcs of infrared emission…
Understanding the star formation process is central to much of modern astrophysics. For several decades it has been thought that stellar birth is primarily controlled by the interplay between gravity and magnetostatic support, modulated by…
The observed rapid onset of star formation in molecular clouds requires rapid formation of dense fragments which can collapse individually before being overtaken by global gravitationally-driven flows. Many previous investigations have…
Most stars will experience episodes of substantial mass loss at some point in their lives. For very massive stars, mass loss dominates their evolution, although the mass loss rates are not known exactly, particularly once the star has left…
Gas accretion, hot ($\sim 10^6\,{\rm K}$) atmospheres, and a tilt between the rotation axes of the disc and the atmosphere are all common predictions of standard galaxy evolution theory for massive star-forming galaxies at low redshift.…
It is argued that galaxies like ours sustain their star formation by transferring gas from an extensive corona to the star-forming disc. The transfer is effected by the galactic fountain -- cool clouds that are shot up from the plane to…
We present a theoretical model for primordial star formation. First we describe the structure of the initial gas cores as virialized, quasi-hydrostatic objects in accord with recent high resolution numerical studies. The accretion rate can…
Our adaptive optics observations of nearby AGN at spatial resolutions as small as 0.085arcsec show strong evidence for recent, but no longer active, nuclear star formation. We begin by describing observations that highlight two contrasting…
There is overwhelming evidence that the Milky Way has formed its stars at a rel- atively constant rate throughout the Hubble time. This implies that its stock of cold gas was not in place since the beginning but it has been acquired slowly…
Star formation is thought to be triggered by gravitational collapse of the dense cores of molecular clouds. Angular momentum conservation during the collapse results in the progressive increase of the centrifugal force, which eventually…
We present numerical evidence of dynamic star formation in which the accreted stellar mass grows superlinearly with time, roughly as $t^2$. We perform simulations of star formation in self-gravitating hydrodynamic and magneto-hydrodynamic…
We study the impact of stellar winds and supernovae on the multi-phase interstellar medium using three-dimensional hydrodynamical simulations carried out with FLASH. The selected galactic disc region has a size of (500 pc)$^2$ x $\pm$ 5 kpc…
Massive stars drive the evolution of the interstellar medium through their radiative and mechanical energy input. After their birth, they form bubbles of hot gas surrounded by a dense shell. Traditionally, the formation of bubbles is…
We propose that star formation is delayed relative to the inflow rate in rapidly-accreting galaxies at very high redshift (z > 2) because of the energy conveyed by the accreting gas. Accreting gas streams provide fuel for star formation,…
In the multi-scale view of the star formation process the material flows from large molecular clouds down to clumps and cores. In this paradigm it is still unclear if it is gravity or turbulence that drives the observed supersonic…
We present a series of numerical studies of the interaction of colliding radiative, hydrodynamic young stellar outflows. We study the effect of the collision impact parameter on the acceleration of ambient material and the degree to which…
We present two dimensional hydrodynamic calculations of free expanding supergalactic winds, taking into consideration strong radiative cooling. Our main premise is that supergalactic winds are powered by collections of superstar clusters.…