“Simulated molecular clouds are beautiful, intricate, and ever-changing — properties that make them ideal candidates for high-powered visualization,” wrote Erica Kaminski, a PhD student in the Department of Physics and Astronomy, when she submitted these winning images to the data visualization contest sponsored by the Health Sciences Center for Computational Innovation (HSCCI). The contest helped showcase the capabilities of the new VISTA Collaboratory in Carlson Library — and in this case the Center for Integrated Research Computing’s Blue Gene/Q system, called Blue Streak, which consists of 1,024 nodes,16 TB of RAM, and 400 TB of storage.
A molecular cloud (or stellar nursery if star formation is occurring within it) is a type of interstellar cloud whose density and size permit the formation of molecules, most commonly molecular hydrogen — in contrast to other interstellar areas that contain predominantly ionized gas.
“Using Blue Streak, we have just completed a set of high resolution (2000∧3 cells) adaptive mesh refinement simulations to study how these stellar nurseries form,” Kaminski explains. “The simulations are of two large scale streams of gas (~120 light years in diameter) colliding in a 3-dimensional box, under the influence of magnetic fields, gravity, and various thermal processes. Over the 20 million years inside of the simulation box, fluid instabilities form that produce long dense filaments in the gas — structures that behave like and bear striking resemblance to the molecular clouds we find in nature.”
To illustrate the complex network of structures formed in these simulations, two example images from the recent work are shown above. The image above shows a 3D density contour plot of the collision region at 10 million years, with magnetic field lines overlaid on only half of the plot for simplicity. By this time, dense coherent structures are forming out of the flow, as can be seen from the color variation of the various shells — density increases from red to green to blue to magenta in color.
“These structures are undergoing gravitational collapse, dragging magnetic field lines down with them,” Kaminski notes. “This leads to a highly tangled field that is not only beautiful to behold, but can also reveal a great deal about the role magnetic fields play in molecular cloud evolution. The relationship between magnetic fields and star formation is a current popular area of research, and studying the field morphology using high resolution simulations such as these can provide important clues in addressing this link.”
Column density maps of the data are shown in the image below, which depicts number density integrated along a given line of sight through the simulation box.
In this way the 3D data is projected onto a 2D surface, which mimics the way observational astronomers ‘see’ structure on the plane of the sky. The left CDM is a ‘down-the-barrel’ perspective of the colliding flows, while the CDM on the right is a perpendicular view. Here, density increases with color, going from black to red, and reaching densities high enough in the red regions for star formation to occur. “The structures that form in these flows are highly turbulent and filamentary, properties akin to the molecular clouds we observe in local star forming regions,” Kaminski notes. This snapshot was taken 20 million years into the simulation.