Ribbons of the Cosmic Web

The notion that galaxies congregate into ribbons, now known as the cosmic web, was first proposed in 1985 during the Redshift Survey at the Harvard-Smithsonian Center for Astrophysics. Over the last three decades, further mapping has confirmed the existence of these filaments, which lie at the edges of vast cosmic voids.

However, detecting the gas that binds these galaxies is challenging due to its extremely low density. Researchers from UC Santa Cruz turned their attention to the growth patterns of P. polycephalum to better understand these galactic formations and uncover the elusive gas.

The slime mold species at the heart of this investigation typically thrives on decaying organic matter, such as rotting wood and leaves, and can occasionally create noticeable patches on lawns. Remarkably, it is adept at forming efficient networks. In one experiment, researchers positioned food sources to represent major cities around Tokyo, and P. polycephalum quickly established a network that mirrored Japan's rail system.

An algorithm that modeled the growth of the slime mold was fed the coordinates of 37,000 galaxies located within 300 million light-years of the Milky Way, as cataloged by the Sloan Digital Sky Survey. When this model was expanded from a two-dimensional plane to three dimensions, it generated a map illustrating the cosmic web's layout in our vicinity.

“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 explained.

Investigating the Cosmic Web's Structure

Following the Big Bang, the universe expanded, leading to the formation of matter, stars, and galaxies. These stellar families grouped into ribbons, interconnected by tenuous gas clouds.

Astronomers have studied light from quasars located billions of light-years behind these cosmic ribbons. The light emitted from these energetic galactic cores, observed in archival data from the Hubble Space Telescope, displayed indicators of interaction with hydrogen gas that comprises these cosmic filaments.

Wherever the slime mold model predicted the presence of a ribbon, researchers detected gas. The concentration of this gas was highest near the centers of the ribbons, aligning with predictions. The signal from these regions dropped out where gas was most abundant, consistent with the heating of gas that strips electrons from atoms, thus eliminating the absorption spectra.

“By applying our technique to galaxy and absorption-line surveys of the local universe, we demonstrate that the bulk of the Intergalactic Medium (IGM) indeed resides in the cosmic web,” the researchers noted in a study published in The Astrophysical Journal Letters.

Interestingly, these primitive slime molds have been utilized in studies unrelated to biology. Their networks have been employed to model traffic flow in metropolitan areas, solve mazes, and even devise evacuation routes.

“It’s truly remarkable that one of the simplest life forms provides insights into the largest structures in the universe,” remarked Joseph Burchett of UC Santa Cruz, the study's lead researcher.

The lessons we can glean from these simple organisms extend even to our understanding of the universe's most colossal structures.

James Maynard is the founder and publisher of The Cosmic Companion. He hails from New England but now resides in Tucson with his wife, Nicole, and their cat, Max.

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