Dynamical instability is shown to occur in differentially rotating polytropes with and . N p 3.33T/FWF տ 0.14 This instability has a strong mode, although the , 3, and 4 modes also appear. Such instability may m p 1 m p 2 allow a centrifugally hung core to begin collapsing to neutron star densities on a dynamical timescale. The gravitational radiation emitted by such unstable cores may be detectable with advanced ground-based detectors, such as LIGO-II. If the instability occurs in a supermassive star, it may produce gravitational radiation detectable by the spacebased detector LISA.

Gravitational-wave emission from stellar collapse has been studied for nearly four decades. Current state-of-the-art numerical investigations of collapse include those that use progenitors with more realistic angular momentum profiles, properly treat microphysics issues, account for general relativity, and examine non-axisymmetric effects in three dimensions. Such simulations predict that gravitational waves from various phenomena associated with gravitational collapse could be detectable with ground-based and space-based interferometric observatories. This review covers the entire range of stellar collapse sources of gravitational waves: from the accretion-induced collapse of a white dwarf through the collapse down to neutron stars or black holes of massive stars to the collapse of supermassive stars.Electronic Supplementary MaterialSupplementary material is available for this article at 10.12942/lrr-2011-1.

We study the origin of Na i absorbing gas in ultraluminous infrared galaxies motivated by the recent observations by Martin of extremely superthermal linewidths in this cool gas. We model the effects of repeated supernova explosions driving supershells in the central regions of molecular disks with M d = 10 10 M ⊙ , using cylindrically symmetric gas dynamical simulations run with ZEUS-3D. The shocked swept-up shells quickly cool and fragment by Rayleigh-Taylor instability as they accelerate out of the dense, stratified disks. The numerical resolution of the cooling and compression at the shock fronts determines the peak shell density, and so the speed of Rayleigh-Taylor fragmentation. We identify cooled shells and shell fragments as Na i absorbing gas and study its kinematics along various sightlines across the grid. We find that simulations with a numerical resolution of ≤ 0.2 pc produce multiple Rayleigh-Taylor fragmented shells in a given line of sight that appear to explain the observed kinematics. We suggest that the observed wide Na i absorption lines, v = 320 ± 120 km s −1 are produced by these multiple fragmented shells traveling at different velocities. We also suggest that some shell fragments can be accelerated above the observed average terminal velocity of 750 km s −1 by the same energy-driven wind with an instantaneous starburst of ∼ 10 9 M ⊙ . The mass carried by these fragments is only a 6 Packard Fellow 7 Alfred P. Sloan Foundation Fellow Recently, Cooper et al. (2008) performed three-dimensional (3D) simulations of starburst blowout through a galactic disk with a fractal density distribution. They injected energy at a rate proportional to local density, rather than identifying supernova sites and following the

Compact astrophysical objects that rotate rapidly may encounter the dynamical "bar instability." The bar-like deformation induced by this rotational instability causes the object to become a potentially strong source of gravitational radiation. We have carried out a set of long-duration simulations of the bar instability with two Eulerian hydrodynamics codes. Our results indicate that the remnant of this instability is a persistent bar-like structure that emits a long-lived gravitational radiation signal.

Gravitational wave emission from stellar collapse has been studied for more than three decades. Current state-of-the-art numerical investigations of collapse include those that use progenitors with more realistic angular momentum profiles, properly treat microphysics issues, account for general relativity, and examine non-axisymmetric effects in three dimensions. Such simulations predict that gravitational waves from various phenomena associated with gravitational collapse could be detectable with ground-based and space-based interferometric observatories. This review covers the entire range of stellar collapse sources of gravitational waves: from the accretion induced collapse of a white dwarf through the collapse down to neutron stars or black holes of massive stars to the collapse of supermassive stars.Electronic Supplementary MaterialSupplementary material is available for this article at 10.12942/lrr-2003-2.