From slime to space

The idea to use a slime-based algorithm to map the cosmic web came from co-author Oskar Elek, a UC Santa Cruz computational media post-doc. He had previously seen the work of slime mold algorithms, so he urged Joe Burchett — an astronomer at UC Santa Cruz and lead author of the new paper — to apply it to his work on the cosmic web, whose structure remains elusive.

“He actually sent me screenshots of the data fitted with this final algorithm,” Burchett says. “What I saw was a trace of the reconstruction of the cosmic web that appealed much, much, much more to my intuitive sense of what the cosmic web should look like [compared to previous models].”

This isn’t the first time scientists have used slime molds to map various structures. Slime molds are expert filament builders, constructing complex underground networks that help them search for food and resources. These single-celled organisms work as one large colony that can be up to 1 foot (0.3 meters) in diameter. And oddly, their filamentary structures show a propensity for what could be described as problem solving.

Slime molds are adept at “shortest path” problems, such as finding the best way to weave through a maze to locate food hidden within. It’s been called “slime mold computing” before, and even likened to a rudimentary intelligence — though this obviously comes with its own subset of thorny questions.

“For a slime mold, the world is a combination of two fields: gradients of attractants [stuff it wants] and gradients of repellents [stuff it avoids],” Andrew Adamatzky, a professor in unconventional computing at the University of West England wrote in an email. “The slime mold simply follows the gradients. This is how it calculates, for example, the shortest path.”

By tracking how the slime mold algorithm connected separate galaxies, researchers knew where to look for cosmic web filaments in archived observations. “Wherever we saw a filament in our model,” Burchett said in a statement, “the Hubble spectra showed a gas signal, and the signal got stronger toward the middle of filaments where the gas should be denser.” This means the researchers not only used the algorithm to effectively pinpoint where threads of the cosmic web should be, but also actually find them.

“For the first time now, we can quantify the density of the intergalactic medium from the remote outskirts of cosmic web filaments to the hot, dense interiors of galaxy clusters,” Burchett said. “These results not only confirm the structure of the cosmic web predicted by cosmological models, they also give us a way to improve our understanding of galaxy evolution by connecting it with the gas reservoirs out of which galaxies form.”

The new research was published March 10 in The Astrophysical Journal Letters.