Astronomers are using the food-seeking behavior of a tiny cell to map the universe’s huge cosmic web, including dark matter.

Key takeaways

  • Scientists use the food-seeking behavior of a brainless, single-celled creature to map the cosmic web, the universe’s biggest and most mysterious structure.
  • The cosmic web is a vast network of dark matter and gas filaments that link galaxies and galaxy clusters, spanning hundreds of millions of light-years.
  • Researchers used an algorithm based on slime mold’s food-seeking patterns to map the invisible filaments of the cosmic web, providing a 3D model of galaxy connections.
  • The gas between galaxies, essential for star formation, acts as “cosmic food.” The model helps predict how galaxies create stars based on their connections within the cosmic web.
  • The slime mold-based method allowed scientists to identify gas signals in the cosmic web, confirming its structure and enhancing our understanding of galaxy evolution.
This snapshot of a detailed computer simulation (unrelated to this study) shows the complex structure of the cosmic web. Long filaments of dark matter (blue) connect knots of galaxies and galaxy clusters (pink), while gas (orange) permeates throughout. By modeling and observing the cosmic web, researchers are gaining insights into the structure and evolution of the early universe.

A brainless, single-celled creature with a penchant for locating food is assisting astronomers in their study of the universe’s biggest and most enigmatic structure, the cosmic web. But first, things may become a little slimy.

The cosmic web is a massive network of interconnecting filaments consisting of dark matter and gas that serves as the framework for the whole cosmos. These filaments may span hundreds of millions of light-years and connect galaxies, galaxy clusters, and even galaxy superclusters together. However, since the cosmic web is so faint—and the dark matter inside it does not interact with light—it is exceedingly difficult to trace.

To address this difficulty, astronomers at the University of California, Santa Cruz looked through historical data for over 37,000 galaxies before calculating their locations in the sky. They then used a complex computer to map the invisible filaments of gas and dark matter that connect those galaxies, determining how they interact with one another and how the cosmic web drives star formation in these galaxies.

But this was not your typical algorithm. Instead, the researchers based their model on slime mold, namely the species Physarum polycephalum.

This algorithm replicates the mold’s food-seeking activity, sending out tendrils of reconnaissance mold to look for nearby food. If a particular mold thread comes across food, it flourishes, forming a tight bond between the food and the rest of the colony.

By replacing individual galaxies for the mold-based algorithm’s “food,” researchers were able to create a 3D model that depicts how the cosmic web’s galaxy-connecting filaments are linked.

In addition, the gas between galaxies serves as “cosmic food” for star formation. And if you understand how cosmic web filaments are linked to a galaxy, you can make an educated judgment about how quickly or slowly the galaxy is creating stars. This forecast is based on whether or not a galaxy is connected to the cosmic web, as well as how closely related it is to other galaxies. If it is too tightly attached, it risks limiting prospects for star formation; if it is too loosely connected, it will not have access to enough fuel.

Researchers seeded an algorithm inspired by the food-seeking behavior of slime mold with the positions of about 37,000 galaxies, where the galaxies served as the “food.” This helped them model and create a 3D map of the cosmic web connecting these galaxies. Above, the galaxies (or food) are shown in yellow, while the cosmic web is shown in purple. NASA/ESA/J. Burchett and O. Elek (UC Santa Cruz)

From Slime to Space

Co-author Oskar Elek, a computational media post-doc at UC Santa Cruz, proposed using a slime-based algorithm to map the cosmic web. He had already seen the work of slime mold algorithms, so he encouraged Joe Burchett, an astronomer at UC Santa Cruz and lead author of the current publication, to apply it to his research on the cosmic web, whose structure is yet unknown.

“He actually sent me screenshots of the data fitted with this final algorithm,” adds Burchett. “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 employed slime molds to map diverse structures. Slime molds are skilled filament builders, creating intricate subterranean networks to assist them find food and resources. These single-celled creatures form a huge colony that can measure up to one foot (0.3 meters) in diameter. Strangely, their filamentary formations have a proclivity for what could be termed as problem resolution.

Slime molds excel at “shortest path” challenges, such as determining the quickest route through a maze to get food buried within. It’s been dubbed “slime mold computing” and even compared to basic intelligence, though this clearly raises its own set of difficult concerns.

“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 of unconventional computing at the University of West England, wrote in an email. “The slime mold just followed the gradients. This is how it determines, for example, the quickest path.”

Researchers knew where to hunt for cosmic web filaments in archival images after observing how the slime mold algorithm connected different galaxies. “Wherever we saw a filament in our model,” Burchett stated in a release, “the Hubble spectra showed a gas signal, and the signal got stronger toward the middle of filaments where the gas should be denser.” This implies the researchers not only utilized the algorithm to effectively determine where strands of the cosmic web should reside, but they also found.

“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 stated. “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 findings were reported in The Astrophysical Journal Letters.

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