Tyler O'Neal, Staff Editor

Astronomers use slime mold supercomputer simulations to map dark matter holding universe together

The behavior of one of nature's humblest creatures is helping astronomers probe the largest structures in the universe.

The single-cell organism, known as slime mold (Physarum polycephalum), builds complex filamentary networks in search of food, finding near-optimal pathways to connect different locations. In shaping the universe, gravity builds a vast cobweb structure of filaments tying galaxies and clusters of galaxies together along faint bridges hundreds of millions of light-years long. There is an uncanny resemblance between the two networks: one crafted by biological evolution, and the other by the primordial force of gravity.

The cosmic web is the large-scale backbone of the cosmos, consisting primarily of the mysterious substance known as dark matter and laced with gas, upon which galaxies are built. Dark matter cannot be seen, but it makes up the bulk of the universe's material. The existence of a web-like structure to the universe was first hinted at in the 1985 Redshift Survey conducted at the Harvard-Smithsonian Center for Astrophysics. Since those studies, the grand scale of this filamentary structure has grown in subsequent sky surveys. The filaments form the boundaries between large voids in the universe. 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 ({module INSIDE STORY}

But astronomers have had a difficult time finding these elusive strands because the gas is so dim it is hard to detect. Now a team of researchers has turned to slime mold 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.

They designed a computer algorithm, inspired by slime-mold behavior, and tested it against a supercomputer simulation of the growth of dark matter filaments in the universe. A computer algorithm is similar to a recipe that tells a supercomputer precisely what steps to take to solve a problem.

The researchers then applied the slime mold algorithm to data containing the locations of 37,000 galaxies mapped by the Sloan Digital Sky Survey at distances corresponding to 300 million light-years. The algorithm produced a three-dimensional map of the underlying cosmic web structure.

They then analyzed the ultraviolet light from 350 quasars (at much farther distances of billions of light-years) cataloged in the Hubble Spectroscopic Legacy Archive, which holds the data from NASA's Hubble Space Telescope's spectrographs. These distant cosmic flashlights are the brilliant black-hole-powered cores of active galaxies, whose light shines across space and through the foreground cosmic web. Imprinted on that light was the telltale absorption signature of otherwise undetected hydrogen gas that the team analyzed at specific points along the filaments. These target locations are far from the galaxies, which allowed the research team to link the gas to the universe's large-scale 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," said lead researcher Joseph Burchett of the University of California (UC), Santa Cruz. "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. 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 further validates research that denser regions of intergalactic gas are organized into filaments that the team found stretches over 10 million light-years from galaxies. (That distance is more than 100 times the diameter of our Milky Way galaxy.)

The researchers turned to slime mold simulations when they were searching for a way to visualize the theorized connection between the cosmic web structure and the cool gas detected in previous Hubble spectroscopic studies.

Then team member Oskar Elek, a computational media scientist at UC Santa Cruz, discovered online the work of Sage Jenson, a Berlin-based media artist. Among Jenson's works were mesmerizing artistic visualizations showing the growth of a slime mold's tentacle-like network of food-seeking structures. Jenson's art was based on outside scientific research, which detailed an algorithm for simulating the growth of slime mold.

The research team noted a striking similarity between how the slime mold builds complex filaments to capture new food, and how gravity, in shaping the universe, constructs the cosmic web strands between galaxies and galaxy clusters.

Based on the simulation, Elek developed a three-dimensional supercomputer model of the buildup of slime mold to estimate the location of the cosmic web's filamentary structure.

Although using a slime-mold-inspired simulation to pinpoint the universe's largest structures may sound bizarre at first, scientists have used supercomputer models of these humble microorganisms, as well as grown them in Petri dishes in a lab, to solve such complex problems as finding the most efficient traffic routes in large cities, solving mazes and pinpointing crowd evacuation routes. "These are hard problems to solve for a human, let alone a computer algorithm," Elek said.

"You can almost see, especially in the map of galaxies in the local universe from the Sloan data, where the filaments should be," Burchett explained. "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."

The researchers say that it is very difficult to design a reliable algorithm for finding the filaments in such a large survey of galaxies. "So it's quite amazing to see that the virtual slime mold gives you a very close approximation in just minutes," Elek explained. "You can literally watch it grow." Just for comparison, growing the organism in a petri dish takes days. Slime mold actually has a very special kind of intelligence for solving this one spatial task. After all, it's critical to its survival.

Spread of mosquito-borne viral diseases linked to climate change

Tyler O'Neal, Staff Editor

European project of the University of Bayreuth studies the influence of biodiversity

As a result of climate change, mosquito-borne viral diseases are penetrating ever further into Europe. A joint project coordinated by the University of Bayreuth is investigating for the first time how this trend is influenced and even controlled by biological diversity within the respective chains of infection. Consequently, the research work focuses on the biodiversity of viruses, vectors, and infected organisms. The European research network "BiodivERsA" will be funding the project to the tune of almost € 1 million over the next three years. CAPTION Spread of the Asian Tiger Mosquito (Aedes albopictus) in Europe. CREDIT Graphic: Nils Tjaden.{module INSIDE STORY}

In addition to the University of Bayreuth, four other institutions are involved in the new research project entitled "DiMoC - Diversity components in mosquito-borne diseases in the face of climate change": the Bernhard Nocht Institute for Tropical Medicine in Hamburg, the Institute for Tropical Medicine in Antwerp, the Institute for Development Research in Montpellier, and the National Autonomous University of Mexico. On 6 March 2020, the first meeting of the project partners took place in the Iwalewahaus of the University of Bayreuth.

In public debate, but also in the scientific community itself, the term "biodiversity" is usually applied to the relative wealth of species in the animal and plant world. The ecological and economic benefits of this diversity, which is threatened by climate change, have been clearly proven by scientific research. However, very little is known about the impact of biodiversity, for example in the area of diseases caused by arboviruses. These are viruses that are transmitted in particular by mosquitoes, ticks, fleas, or midges. These vectors, also comprise a large number of species, which may help determine the routes of transmission and the probability of infection.

"So, in our research project, we want to get to the bottom of the question of how chains of infection - from arboviruses to diseased organisms - develop under the influence of biological diversity. In this way, we will gain more precise insights into the causes and pathways by which some of the viral diseases transmitted by mosquitoes spread from the tropics to Europe. On the basis of these research results, well-founded recommendations for action can be developed, for example for health, environmental, and development policy," explains Prof. Dr. Carl Beierkuhnlein, who is the Chair of Biodiversity at the University of Bayreuth and coordinates the DiMoC project.

The aim is to produce a broadly based and scientifically sound report. It will be addressed to all those who can help to prevent or contain infectious diseases transmitted by mosquitoes. These include not least the diseases caused by the West Nile virus and the Chikungunya virus. The vector of the Chikungunya virus is the Asian tiger mosquito, which thanks to international trade has reached southern Europe. In Germany, too, it is finding increasingly favourable living conditions. The planned guide will therefore take into account both current climatic conditions and projections of future climate change.

A central aim of the research project is to develop reliable risk assessments through empirical studies and model calculations. To this end, supercomputer simulations will be used to develop and compare different future scenarios. These calculations will take into account not only the identified impact of biodiversity on chains of infection, but also, for example, that of landscape diversity and prevailing socio-economic conditions. "It is precisely this point that illustrates how important the close interdisciplinary cooperation in our project is. The participating partner institutions contribute very different expertise to the research work - that from medicine, the natural, environmental and geosciences, but also from the social sciences," says Dr. Stephanie Thomas, who coordinates the elite study programme "Global Change Ecology" at the University of Bayreuth and is involved in the DiMoC project from a biogeographic angle.

Supercomputing shows safety zone saves giant moons from fatal plunge

Tyler O'Neal, Staff Editor

Numerical simulations have shown that the temperature gradient in the disk of gas around a young gas giant planet could play a critical role in the development of a satellite system dominated by a single large moon, similar to Titan around Saturn. Researchers found that dust in the circumplanetary disk can create a "safety zone," which keeps the moon from falling into the planet as the system evolves.

Astronomers believe that many of the moons we see in the Solar System, especially large moons, formed along with the parent planet. In this scenario, moons form from the gas and dust spinning around the still-forming planet. But previous simulations have resulted in either all large moons falling into the planet and being swallowed-up or in multiple large moons remaining. The situation we observe around Saturn, with many small moons but only one large moon, does not fit in either of these models.

Yuri Fujii, a Designated Assistant Professor at Nagoya University, and Masahiro Ogihara, a Project Assistant Professor at the National Astronomical Observatory of Japan (NAOJ), created a new model of circumplanetary disks with a more realistic temperature distribution by considering multiple sources of opacities including dust and ice. Then, they simulated the orbital migration of moons considering pressure from disk gas and the gravity of other satellites. An artist's impression of a satellite forming around a giant gas planet which is itself still forming around a star.{module INSIDE STORY}

Their simulations show that there is a "safety zone" where a moon is pushed away from the planet. In this area, warmer gas inside the orbit pushes the satellite outward and prevents it from falling into the planet. 

"We demonstrated for the first time that a system with only one large moon around a giant planet can form," says Fujii. "This is an important milestone to understand the origin of Titan."

But Ogihara cautions, "It would be difficult to examine whether Titan actually experienced this process. Our scenario could be verified through research of satellites around extrasolar planets. If many single-exomoon systems are found, the formation mechanisms of such systems will become a red-hot issue."

These results were published as Fujii and Ogihara "Formation of single-moon systems around gas giants" in Astronomy and Astrophysics Letters in March 2020. The simulations in this research used the PC cluster operated by NAOJ.