Stellar nurseries take form in 3D-printed spheres

Stellar nurseries are vast clouds of gas and dust in which new stars can form under the gravitational influence of denser areas known as “clumps”. Although false-colour photographs and concept art of stellar nurseries are familiar images in popular science, Professor Nia Imara was interested in creating stellar nursery models which captured the complex structural detail of these formations.

Imara made the models using data from simulations of star-forming clouds and a sophisticated 3D printing process in which the fine-scale densities and gradients of the clouds are embedded within a transparent resin. The resulting models are smooth, polished spheres around 8cm in diameter, in which the clouds appear as delicate, swirling clumps and filaments.

“We wanted an interactive object to help us visualise those structures where stars form so we can better understand the physical processes,” said Imara.

Imara, who is an accomplished self-taught artist as well as an astrophysicist, said the idea is an example of science imitating art: “Years ago, I sketched a portrait of myself touching a star. Later, the idea just clicked. Star formation within molecule clouds is my area of expertise, so why not try to build one?”

Imara and her collaborators developed a suite of nine simulations representing different physical conditions within molecular clouds, then turned the data from the simulations into physical objects via high-res, photo-realistic 3D printing, incorporating different materials. While traditional extrusion-based 3D printing can only produce solid objects with a continuous outer surface, they used an inkjet-like process to deposit tiny droplets of opaque resin at precise locations within a surrounding volume of transparent resin, allowing them to build the diffuse shapes in exquisite detail.

Co-author Dr John Forbes said: “Just aesthetically they are really amazing to look at, and then you begin to notice the complex structures that are incredibly difficulty to see with the usual techniques for visualising these simulations.”

For instance, sheet-like or pancake-shaped structures are hard to distinguish in two-dimensional slices or projections, because a section through a sheet simply looks like a filament. Within the spheres, Forbes says, are visible sheets containing little filaments, which is “mindboggling” from the perspective of an astrophysicist trying to understand these evolving structures.

The models also reveal structures which are more continuous than they would appear in two dimensions. Imara explained: “If you have something winding around through space, you might not realize that two regions are connected by the same structure, so having an interactive object you can rotate in your hand allows us to detect these continuities more easily.”

The simulations on which the models are based were designed to investigate the effects of three physical processes that influence the evolution of molecular clouds: turbulence, gravity, and magnetic fields. By playing with these variables, such as the strength of the magnetic fields or how fast the gas is moving, the simulations show the impact on the morphology of substructures related to star formation.

Stars tend to form in clumps and cores located at the intersection of filaments, where the density of gas and dust is great enough for gravity to take over and begin star formation. Imara said: “We think that the spins of these newborn stars will depend on the structures in which they form; stars in the same filament will “know” about each other’s spins.”

The researchers say that the models make it possible for anyone to get a sense of how factors such as gravity influence star formation conditions. They hope that they will serve as tools for education and public outreach; Imara plans to use them in an astrophysics course she will start teaching this autumn.

In future, they may try incorporating additional information through the use of colours and explore 3D printing to represent observational data from nearby molecular clouds, such as those in the constellation Orion.