Consider the cosmos: There are around 100 billion galaxies in the vast universe, all teeming with stars, planets, and dust. The myriad galaxies are connected together through a giant cosmic web made of dark matter, an invisible force that has so far proven impossible to observe directly.
But by looking extremely closely at one single-cell organism here on Earth, scientists think they may have found the ideal analogue to this most massive of cosmic problems.
The organism in question is slime mold. Made up of millions of single-cell creatures, slime mold collectives move and forage for food via a complex network of filaments. The mold's instinctive ability to connect to different locations may enable the creation of the first maps of the universe's web-like structure, a new study suggests.
In the study, published this week in The Astrophysical Journal Letters, scientists use a computer algorithm based on the behavior of slime mold to create a 3-D map of the cosmic web structure.
"It's really fascinating that one of the simplest forms of life actually enables insight into the very largest-scale structures in the universe," Joseph Burchett, a researcher at the University of California, Santa Cruz and lead author of the new study, said in a statement accompanying the research.
Cosmic slime mold
Slime molds may look like something straight out of a science-fiction horror film, but they are completely harmless.
These single-cell organisms creep at a very slow pace of 1 millimeter an hour in search of the dead plants they feed on. And though they are a collection of single-cell creatures, the molds are deceptively intelligent, capable of coming up with the most efficient — and quite complex — route to reaching their goal.
Now, that same power could help resolve one of the biggest mysteries of the universe.
The team designed a computer algorithm based on the organisms’ behavior, and the charted locations of 37,000 galaxies in the universe.
The cosmic web that connects the galaxies and every other structure in the universe is made up of dark matter and gas filaments that feed galaxies and help fuel the birth of their stars. The network of gas filaments is one of the largest structures of the universe, if not the largest.
These threads extend across millions of light years in a web-like formation, separated by giant voids. But despite its size, the gas is quite faint and hard to detect.
Dark matter, meanwhile, is believed to make up around 70 percent of the mass of the universe, but it also cannot be seen. As a result, the cosmic web is practically invisible.
But by running the slime-informed algorithm, the researchers managed to draw up a map of the web of gas filaments that connected the galaxies in the most creative, yet efficient, way possible.
Bringing the dark web to light
The scientists didn’t stop there. They then analyzed the ultraviolet light emitted by 350 quasars, which are essentially extremely large and extremely bright active galactic nuclei — these structures act much like a cosmic flashlight, shining through the foreground of the cosmic web.
The quasars reveal a striking similarity between how slime mold moves in search of food to how gravity arranged the filaments of gas connecting galaxies together.
"The slime-mold model fits that intuition impressively. The structure that you know should be there is all of a sudden found by the computer algorithm,” Burchett said.
“There was no other known method that was well suited to this problem for our research."
The findings compliment other efforts to trace dark matter in the cosmos. One such effort, NASA's WFIRST telescope, is designed to peer into the cosmos and directly observe dark matter for the first time. Currently slated for completion in the mid-2020s, this supposed successor to the Hubble telescope will rely on microlensing — using a nearby galaxy to magnify the cosmos beyond it — to see far into the distant universe.
Abstract: Modern cosmology predicts that matter in our universe today has assembled into a vast network of filamentary structures colloquially termed the "cosmic web." Because this matter is either electromagnetically invisible (i.e., dark) or too diffuse to image in emission, tests of this cosmic web paradigm are limited. Wide-field surveys do reveal web-like structures in the galaxy distribution, but these luminous galaxies represent less than 10% of baryonic matter. Statistics of absorption by the intergalactic medium (IGM) via spectroscopy of distant quasars support the model yet have not conclusively tied the diffuse IGM to the web. Here, we report on a new method inspired by the Physarum polycephalum slime mold that is able to infer the density field of the cosmic web from galaxy surveys. Applying our technique to galaxy and absorption-line surveys of the local universe, we demonstrate that the bulk of the IGM indeed resides in the cosmic web. From the outskirts of cosmic web filaments, at approximately the cosmic mean matter density (ρm ) and ~5 virial radii from nearby galaxies, we detect an increasing H i absorption signature toward higher densities and the circumgalactic medium, to ~200ρm . However, the absorption is suppressed within the densest environments, suggesting shock-heating and ionization deep within filaments and/or feedback processes within galaxies.