Slime mold helps astronomers map the universe’s dark matter
The food-seeking behavior of a simple organism is helping astronomers trace the universe’s vast cosmic web, dark matter and all.
A brainless, single-celled organism with a knack for locating food is assisting astronomers in their study of the universe’s greatest and most mysterious structure — the cosmic web. But first, things might get slimy.
The cosmic web is a massive network of interconnected filaments consisting of dark matter and gas that serves as the foundation for the entire universe. These filaments, which can span hundreds of millions of light-years, connect galaxies, galaxy clusters, and even galaxy superclusters. However, because the cosmic web is so faint and the dark matter within it does not interact with light, mapping it is extremely challenging.
To address this issue, astronomers at the University of California, Santa Cruz looked through historical data for over 37,000 galaxies before calculating their positions in the sky. They then used a complex computer to map out the invisible filaments of gas and dark matter that connect those galaxies in order to understand how they interact with and how the cosmic web drives star formation in these galaxies.
But this was no ordinary algorithm. Instead, the researchers employed a slime mold model, namely the species Physarum polycephalum.
This algorithm mimics the mold’s food-seeking activity, which involves sending out tendrils of reconnaissance mold to look for nearby food. If a specific mold thread comes into contact with food, it thrives, creating a strong bond between the food and the rest of the colony.
Researchers were able to build a 3D map indicating how the galaxy-connecting filaments of the cosmic web are linked by substituting individual galaxies for the mold-based algorithm’s “food.”
In addition, the gas between galaxies serves as a kind of “cosmic food” that stimulates star formation. And if you know how cosmic web filaments are linked to a galaxy, you may make an educated judgment about how fast or slow the galaxy is creating stars. This prediction is based on whether a galaxy is connected to the cosmic web and how strongly bonded it is to other galaxies. If it’s attached too tightly, it risks drying up prospects for star formation; too loosely, it won’t be able to get to enough fuel.
From slime to space
Oskar Elek, a computational media postdoc at UC Santa Cruz, came up with the concept to map the cosmic network using a slime-based algorithm. He had previously observed the work of slime mold algorithms and urged Joe Burchett, an astronomer at UC Santa Cruz and the primary author of the current research, to apply it to his work on the cosmic web, the structure of which remains a mystery.
“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].”
Scientists have previously used slime molds to map diverse structures. Slime molds are skilled filament builders, creating complex underground networks to aid in their search for food and resources. These single-celled creatures form a huge colony that can be up to 1 foot (0.3 meters) across. And, strangely, their filamentary structures exhibit a propensity for problem resolution.
Slime molds excel at “shortest path” challenges, such as figuring out the quickest way to travel a maze to find food hidden within. It’s been dubbed “slime mold computing” and even compared to rudimentary intelligence – though this clearly comes with its own set of difficult 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.”
Researchers knew where to hunt for cosmic web filaments in archived images by observing how the slime mold algorithm connected distant galaxies. “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.”