Constraint on the maximum mass of neutron stars using GW170817 event

We revisit the constraint on the maximum mass of cold spherical neutron stars coming from the observational results of GW170817. We develop a new framework for the analysis by employing both energy and angular momentum conservation laws as well as solid results of latest numerical-relativity simulations and of neutron stars in equilibrium. The new analysis shows that the maximum mass of cold spherical neutron stars can be only weakly constrained as M_{\rm max} \alt 2.3M_\odot. Our present result illustrates that the merger remnant neutron star at the onset of collapse to a black hole is not necessarily rapidly rotating and shows that we have to take into account the angular momentum conservation law to impose the constraint on the maximum mass of neutron stars.Comment: 14 pages, 5 figures, matches the version accepted by PRD for publicatio

Mass Ejection from the Remnant of a Binary Neutron Star Merger: Viscous-Radiation Hydrodynamics Study

We perform long-term general relativistic neutrino radiation hydrodynamics simulations (in axisymmetry) for a massive neutron star (MNS) surrounded by a torus, which is a canonical remnant formed after the binary neutron star merger. We take into account the effects of viscosity, which is likely to arise in the merger remnant due to magnetohydrodynamical turbulence. As the initial condition, we employ the azimuthally averaged data of the MNS-torus system derived in a three-dimensional, numerical-relativity simulation for the binary neutron star merger. The viscous effect plays key roles for the remnant evolution and mass ejection from it in two phases of the evolution. In the first $t\lesssim10$ ms, a differential rotation state of the MNS is changed to a rigidly rotating state, and as a result, a sound wave, which subsequently becomes a shock wave, is formed in the vicinity of the MNS due to the variation of the quasi-equilibrium state of the MNS. The shock wave induces significant mass ejection of mass $\sim(0.5-2.0)\times 10^{-2}M_\odot$ for the alpha viscosity parameter of $0.01-0.04$. For the longer-term evolution with $\sim 0.1-10$ s, a significant fraction of the torus material is ejected. The ejecta mass is likely to be of order $10^{-2}M_\odot$, so that the total mass of the viscosity-driven ejecta could dominate that of the dynamical ejecta of mass $\lesssim 10^{-2}M_\odot$. The electron fraction, $Y_e$, of the ejecta is always high enough ($Y_e\gtrsim0.25$) that this post-merger ejecta is lanthanide-poor; hence, the opacity of the ejecta is likely to be $\sim 10-100$ times lower than that of the dynamical ejecta. This indicates that the electromagnetic signal from the ejecta would be rapidly evolving, bright, and blue if it is observed from a small viewing angle ($\lesssim 45^\circ$) for which the effect of the dynamical ejecta is minor.Comment: 21 pages, 18 figures, accepted for publication in Ap

Toward reliable algorithmic self-assembly of DNA tiles: A fixed-width cellular automaton pattern

Bottom-up fabrication of nanoscale structures relies on chemical processes to direct self-assembly. The complexity, precision, and yield achievable by a one-pot reaction are limited by our ability to encode assembly instructions into the molecules themselves. Nucleic acids provide a platform for investigating these issues, as molecular structure and intramolecular interactions can encode growth rules. Here, we use DNA tiles and DNA origami to grow crystals containing a cellular automaton pattern. In a one-pot annealing reaction, 250 DNA strands first assemble into a set of 10 free tile types and a seed structure, then the free tiles grow algorithmically from the seed according to the automaton rules. In our experiments, crystals grew to ~300 nm long, containing ~300 tiles with an initial assembly error rate of ~1.4% per tile. This work provides evidence that programmable molecular self-assembly may be sufficient to create a wide range of complex objects in one-pot reactions