A new study examining the growth of slime mold could help astronomers understand the development of galaxies in the cosmic web.
Slime mold has a surprising resemblance to groups of galaxies, a new study reveals. By studying the way these primitive lifeforms grow, researchers hope to better understand how and why galaxies form into massive strands that stretch across the Cosmos, forming the largest structures in the Universe.
The single-celled Physarum polycephalum builds complex networks of filaments in its search for food. In doing so, this simple lifeform creates highly-efficient pathways connecting different locations. Like this variety of slime mold, galaxies also formed within thin ribbons millions of light years long, connected by deposits of gasses. The networks completed by galaxies and the primitive organisms have more than a passing resemblance to each other.
On March 31, I will interview Dr. Joe Burchett of The University of California, Santa Cruz, lead researcher on this study, on the Astronomy News with the Cosmic Companion podcast.
Tie a Yellow Ribbon ‘Round the Old Oak Tree
The first realization that galaxies coalesced into ribbons (commonly known as the cosmic web) came in 1985, as part of the Redshift Survey conducted at the Harvard-Smithsonian Center for Astrophysics. Over the last 35 years, additional mapping has shown that these filaments exist at the boundaries between vast voids throughout the Cosmos.
However, the gasses connecting the galaxies within these filaments is exceedingly thin, making observation of these ribbons throughout the Cosmos difficult. Researchers from the University of California Santa Cruz examined the growth of P. polycephalum in an effort to map galaxies, and find the hidden gas.
This slime mold at the center of this study is typically found on rotting logs and on decaying leaves, and can also form yellow patches on lawns. However, this primitive lifeform is also capable of forming highly-efficient networks. in one experiment, researchers put food in positions based on the major cities of Japan near Tokyo. Before long, samples of P. polycephalum formed a network of ribbons reminiscent of the Japanese rail system.
An algorithm modeling growth of the slime mold was provided with the positions of 37,000 galaxies within 300 million light years from the Milky Way, mapped by the Sloan Digital Sky Survey. This model, once extended from two dimensions to three, produced a map showing the cosmic web structure in our region of the Universe.
“It’s somewhat coincidental that it works, but not entirely. A slime mold creates an optimized transport network, finding the most efficient pathways to connect food sources. In the cosmic web, the growth of structure produces networks that are also, in a sense, optimal. The underlying processes are different, but they produce mathematical structures that are analogous,” Burchett stated.
Surfing the Cosmic Web
As the Universe expanded following the Big Bang, energy coalesced into matter, forming stars and galaxies. These families of stars came together into ribbons, linked by tenuous clouds of gas.
Astronomers examined the light coming from quasars sitting billions of light years “behind” these cosmic ribbons. Light from these highly-energetic galactic cores, seen in old data from the Hubble Space Telescope, showed the telltale signs of passing through hydrogen gas which makes up these cosmic tendrils.
Wherever the slime mold model predicted a ribbon would form, researchers found gas. These deposits were more concentrated near their centers, as predicted by models. Where gas was most concentrated, the signal dropped out. This was also expected, as gas in those regions is heated until electrons within the atoms are driven off, eliminating the absorption spectra.
“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,” researchers wrote in a study published in The Astrophysical Journal Letters.
These primitive slime molds have previously been used in studies having nothing to do with biology. The networks have modeled traffic patterns in large cities, have solved mazes, and determined crowd evacuation routes.
“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 of the University of California (UC), Santa Cruz, lead researcher on the study, stated.
There is a lot we can learn from simple mold, even about the largest structures in the Universe.
James Maynard is the founder and publisher of The Cosmic Companion. He is a New England native turned desert rat in Tucson, where he lives with his lovely wife, Nicole, and Max the Cat.
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