Mar 11 2020
Astronomers are now able to explore the largest structures that exist in the universe thanks to the behavior of one of nature’s most unassuming creatures.
Dark Matter Using Slime Mold Algorithm" />
Astronomers have gotten creative in trying to trace the elusive cosmic web, the large-scale backbone of the cosmos. Researchers turned to slime mold, a single-cell organism found on Earth, to help them build a map of the filaments in the local universe (within 500 million light-years from Earth) and find the gas within them. The researchers designed a computer algorithm inspired by the organism’s behavior and applied it to data containing the positions of 37,000 galaxies (“food” for the slime mold) mapped by the Sloan Digital Sky Survey. The algorithm produced a three-dimensional map of the underlying cosmic web’s intricate filamentary network, the purple structure in the image. The three sets of inset boxes show some of those individual galaxies that were “fed” to the slime mold and the filamentary structure connecting them. The galaxies are represented by the yellow dots in three of the inset images. Next to each galaxy snapshot is an image of the galaxies with the cosmic web’s connecting strands (purple) superimposed on them. Image Credit: NASA, ESA, and J. Burchett and O. Elek (University of California, Santa Cruz).
Called slime mold (Physarum polycephalum), the single-cell organism builds intricate filamentary networks to find food and identifies near-optimal pathways to link different locations.
Gravity constructs a huge cobweb structure of filaments, linking galaxies as well as clusters of galaxies along faint bridges while shaping the universe. These bridges stretch to hundreds of millions of light-years. The two networks have an uncanny similarity even though one network is built by biological evolution, and the other is built by gravity’s primordial force.
The large-scale backbone of the cosmos is the elusive cosmic web, which mainly contains the mysterious substance called dark matter and trace amounts of gas, based on which galaxies are constructed.
Although dark matter cannot be visualized, it makes up most of the universe’s material. In 1985, a Redshift Survey was performed at the Harvard-Smithsonian Center for Astrophysics that hinted at the existence of a web-like or filamentary structure in the universe. Since that survey, the grand scale of this web-like structure has increased in later sky surveys. The strands create the boundaries between massive voids present in the universe.
However, astronomers found it difficult to trace these elusive filaments because the gas is so dull that it cannot be detected easily.
Researchers are now studying slime mold in an attempt to construct a map of the elusive filaments in the local universe (that is, within 500 million light-years from Earth) and identify the gas inside them.
Inspired by slime-mold behavior, the researchers eventually developed a computer algorithm and tested it against a computer simulation of the emergence of dark matter filaments within the universe. A computer algorithm is analogous to a recipe that precisely instructs a PC about the steps that need to be taken to solve an issue.
The scientists subsequently applied the slime mold algorithm to data that contained the locations of 37,000 galaxies plotted by the Sloan Digital Sky Survey, at distances matching to 300 million light-years. The computer algorithm generated a three-dimensional (3D) map of the fundamental cosmic web structure.
Later, the team examined the ultraviolet light produced by 350 quasars (at relatively farther distances of billions of light-years). The quasars have been cataloged in the Hubble Spectroscopic Legacy Archive, which contains the data provided by NASA’s Hubble Space Telescope’s spectrographs.
These remote cosmic flashlights represent the vivid black-hole-powered cores of active galaxies. The light from these galaxies illuminates over space and travels via the foreground cosmic web.
The telltale absorption signature of hydrogen gas, which was not detected, was etched on that light. This signature was analyzed by the researchers at certain points along the filaments. Target locations like these are far from the galaxies, which enabled the scientists to connect the gas to the large-scale structure of the universe.
It’s really fascinating that one of the simplest forms of life actually enables insight into the very largest-scale structures in the universe. By using the slime-mold simulation to find the location of the cosmic web filaments, including those far from galaxies, we could then use the Hubble Space Telescope’s archival data to detect and determine the density of the cool gas on the very outskirts of those invisible filaments.
Joseph Burchett, Lead Researcher, University of California, Santa Cruz
Burchett continued, “Scientists have detected signatures of this gas for several decades, and we have proven the theoretical expectation that this gas comprises the cosmic web.”
The survey also validated studies that within the intergalactic gas, denser areas are arranged into filaments, and the researchers discovered that these filaments stretch more than 10 million light-years from galaxies. (That distance is over 100 times the diameter of the Milky Way galaxy.)
The scientists eventually turned to the simulations of slime mold when they were exploring ways to view the theorized relationship between the cool gas identified in earlier Hubble spectroscopic studies and the cosmic web structure.
Oskar Elek, a team member and a computational media scientist at the University of California, Santa Cruz (UC Santa Cruz) discovered the work of a Berlin-based media artist, Sage Jenson, online.
Among Jenson’s studies were captivating artistic visualizations that displayed the growth of a tentacle-like network of food-seeking structures of slime mold. Jenson’s art was based on scientific research that described an algorithm for replicating the growth of slime mold.
The scientists observed a distinct similarity between how gravity, in molding the universe, builds the cosmic web strands between galaxies and clusters of galaxies, and how the slime mold constructs complex filaments to trap new food.
On the basis of this simulation, Elek created a 3D computer model of the accumulation of slime mold to predict the location of the filamentary structure of the cosmic web.
It may appear strange to use a slime-mold-inspired simulation to highlight the largest structures in the universe, but researchers have utilized computer models of these humble pathogens and also cultured them in Petri dishes in a laboratory, to overcome challenging issues, like solving mazes, identifying the most efficient traffic routes in huge cities, and pinpointing the evacuation routes for crowds.
“These are hard problems to solve for a human, let alone a computer algorithm,” stated Elek.
You can almost see, especially in the map of galaxies in the local universe from the Sloan data, where the filaments should be. 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. There was no other known method that was well suited to this problem for our research.
Joseph Burchett, Lead Researcher, University of California, Santa Cruz
According to the team, it is not easy to develop a consistent algorithm to locate the filaments in such a huge survey of galaxies.
So it’s quite amazing to see that the virtual slime mold gives you a very close approximation in just minutes. You can literally watch it grow.
Oskar Elek. Team Member and Computational Media Scientist, University of California, Santa Cruz
For comparison purposes, it can take days to grow the microorganism in a Petri dish. In fact, slime mold has a very unique kind of intelligence for resolving this one spatial job. After all, it is important for its survival.
The researchers’ study will be published in The Astrophysical Journal Letters.