The formation of filamentary bundles in turbulent molecular clouds

The classical picture of a star-forming filament is a near-equilibrium structure, with collapse dependent on its gravitational criticality. Recent observations have complicated this picture, revealing filaments as a mess of apparently interacting subfilaments, with transsonic internal velocity dispersions and mildly supersonic intra-subfilament dispersions. How structures like this form is unresolved. Here we study the velocity structure of filamentary regions in a simulation of a turbulent molecular cloud. We present two main findings: first, the observed complex velocity features in filaments arise naturally in self gravitating hydrodynamic simulations of turbulent clouds without the need for magnetic or other effects. Second, a region that is filamentary only in projection and is in fact made of spatially distinct features can displays these same velocity characteristics. The fact that these disjoint structures can masquerade as coherent filaments in both projection and velocity diagnostics highlights the need to continue developing sophisticated filamentary analysis techniques for star formation observations.Comment: Undergoing revision for ApJ; comments are welcome. A very similar set of data to the one presented here can be interacted with at http://nickolas1.com/filamentvelocities

Symmetric Regularization, Reduction and Blow-Up of the Planar Three-Body Problem

We carry out a sequence of coordinate changes for the planar three-body problem which successively eliminate the translation and rotation symmetries, regularize all three double collision singularities and blow-up the triple collision. Parametrizing the configurations by the three relative position vectors maintains the symmetry among the masses and simplifies the regularization of binary collisions. Using size and shape coordinates facilitates the reduction by rotations and the blow-up of triple collision while emphasizing the role of the shape sphere. By using homogeneous coordinates to describe Hamiltonian systems whose configurations spaces are spheres or projective spaces, we are able to take a modern, global approach to these familiar problems. We also show how to obtain the reduced and regularized differential equations in several convenient local coordinates systems.Comment: 51 pages, 4 figure

A thrust-sheet propulsion concept using fissionable elements

A space propulsion concept is proposed and analyzed which consists of a thin sheet coated on one side with fissionable material, so that nuclear power is converted directly into propulsive power. Thrust is available both from ejected fission fragments and from thermal radiation. Optimum thicknesses are determined for the active and substrate layers. This concept is shown to have potential mission capability (in terms of velocity increments) superior to that of all other advanced propulsion concepts for which performance estimates are available. A suitable spontaneously fissioning material such as Cf254 could provide an extremely high-performance first stage beyond earth orbit. In contrast with some other advanced nuclear propulsion concepts, there is no minimum size below which this concept is infeasible

Electro-thermal rocket Patent

Electrothermal rocket engine using resistance heated heat exchange

Do all stars in the solar neighbourhood form in clusters? A cautionary note on the use of the distribution of surface densities

Bressert et al. recently showed that the surface density distribution of low-mass, young stellar objects (YSOs) in the solar neighbourhood is approximately log-normal. The authors conclude that the star formation process is hierarchical and that only a small fraction of stars form in dense star clusters. Here, we show that the peak and the width of the density distribution are also what follow if all stars form in bound clusters which are not significantly affected by the presence of gas and expand by two-body relaxation. The peak of the surface density distribution is simply obtained from the typical ages (few Myr) and cluster membership number (few hundred) typifying nearby star-forming regions. This result depends weakly on initial cluster sizes, provided that they are sufficiently dense (initial half mass radius of <0.3 pc) for dynamical evolution to be important at an age of a few Myr. We conclude that the degeneracy of the YSO surface density distribution complicates its use as a diagnostic of the stellar formation environment.Comment: 5 pages, 3 figures, MNRAS Letter; Updated to match final journal styl