Very fast optical flaring from a possible new Galactic magnetar.

Highly luminous rapid flares are characteristic of processes around compact objects like white dwarfs, neutron stars and black holes. In the high-energy regime of X-rays and gamma-rays, outbursts with variabilities on timescales of seconds or less are routinely observed, for example in gamma-ray bursts or soft gamma-ray repeaters. At optical wavelengths, flaring activity on such timescales has not been observed, other than from the prompt phase of one exceptional gamma-ray burst.

Shear instability in fluids with a density-dependent viscosity.

We present a shear instability, which can be triggered in compressible fluids with density-dependent viscosity at shear rates above critical. The instability mechanism is generic: It is based on density-dependent viscosity, compressibility, as well as flow two-(three-)dimensionality that provides coupling between streamwise and transversal velocity components and density variations. The only factor stabilizing the instability is fluid elasticity.

Discovery of the progenitor of the type Ia supernova 2007on.

Type Ia supernovae are exploding stars that are used to measure the accelerated expansion of the Universe and are responsible for most of the iron ever produced. Although there is general agreement that the exploding star is a white dwarf in a binary system, the exact configuration and trigger of the explosion is unclear, which could hamper their use for precision cosmology. Two families of progenitor models have been proposed.

Kinetic characterization of strongly coupled systems.

We propose a simple method to determine the local coupling strength Gamma experimentally, by linking the individual particle dynamics with the local density and crystal structure of a 2D plasma crystal. By measuring particle trajectories with high spatial and temporal resolution we obtain the first maps of Gamma and temperature at individual particle resolution. We employ numerical simulations to test this new method, and discuss the implications to characterize strongly coupled systems.

Highly resolved fluid flows: "liquid plasmas" at the kinetic level.

Fluid flow around an obstacle was observed at the kinetic (individual particle) level using "complex (dusty) plasmas" in their liquid state. These "liquid plasmas" have bulk properties similar to water (e.g.

Rapid large-scale magnetic-field dissipation in a collisionless current sheet via coupling between Kelvin-Helmholtz and lower-hybrid drift instabilities.

Rapid large-scale magnetic-field dissipation is observed in a full kinetic simulation of cross-field current instabilities in a current sheet even when the thickness of the current sheet is at ion scale. The Kelvin-Helmholtz instability caused by the velocity shear between the current-carrying ions and the cold background ions excites the lower-hybrid drift instability at the edges of the undulated current sheet. We show that the nonlinear coupling between these two instabilities is responsible for the observed rapid dissipation.