One puzzle in question is the “Hubble tension,” which refers to a mismatch in measurements of how fast the universe is expanding. The other involves observations of numerous early, bright galaxies that existed at a time when the early universe should have been much less populated.

Now, the MIT team has found that both puzzles could be resolved if the early universe had one extra, fleeting ingredient: early dark energy. Dark energy is an unknown form of energy that physicists suspect is driving the expansion of the universe today. Early dark energy is a similar, hypothetical phenomenon that may have made only a brief appearance, influencing the expansion of the universe in its first moments before disappearing entirely.

Some physicists have suspected that early dark energy could be the key to solving the Hubble tension, as the mysterious force could accelerate the early expansion of the universe by an amount that would resolve the measurement mismatch.

The MIT researchers have now found that early dark energy could also explain the baffling number of bright galaxies that astronomers have observed in the early universe. In their new study, reported in the Monthly Notices of the Royal Astronomical Society, the team modeled the formation of galaxies in the universe’s first few hundred million years. When they incorporated a dark energy component only in that earliest sliver of time, they found the number of galaxies that arose from the primordial environment bloomed to fit astronomers’ observations.

“You have these two looming open-ended puzzles,” says study co-author Rohan Naidu, a postdoc in MIT’s Kavli Institute for Astrophysics and Space Research. “We find that in fact, early dark energy is a very elegant and sparse solution to two of the most pressing problems in cosmology.”

The study’s co-authors include lead author and Kavli postdoc Xuejian (Jacob) Shen, and MIT professor of physics Mark Vogelsberger, along with Michael Boylan-Kolchin at the University of Texas at Austin, and Sandro Tacchella at the University of Cambridge.

Big city lights

Based on standard cosmological and galaxy formation models, the universe should have taken its time spinning up the first galaxies. It would have taken billions of years for primordial gas to coalesce into galaxies as large and bright as the Milky Way.

But in 2023, NASA’s James Webb Space Telescope (JWST) made a startling observation. With an ability to peer farther back in time than any observatory to date, the telescope uncovered a surprising number of bright galaxies as large as the modern Milky Way within the first 500 million years, when the universe was just 3 percent of its current age.

“The bright galaxies that JWST saw would be like seeing a clustering of lights around big cities, whereas theory predicts something like the light around more rural settings like Yellowstone National Park,” Shen says. “And we don’t expect that clustering of light so early on.”

For physicists, the observations imply that there is either something fundamentally wrong with the physics underlying the models or a missing ingredient in the early universe that scientists have not accounted for. The MIT team explored the possibility of the latter, and whether the missing ingredient might be early dark energy.

Physicists have proposed that early dark energy is a sort of antigravitational force that is turned on only at very early times. This force would counteract gravity’s inward pull and accelerate the early expansion of the universe, in a way that would resolve the mismatch in measurements. Early dark energy, therefore, is considered the most likely solution to the Hubble tension.

Galaxy skeleton

The MIT team explored whether early dark energy could also be the key to explaining the unexpected population of large, bright galaxies detected by JWST. In their new study, the physicists considered how early dark energy might affect the early structure of the universe that gave rise to the first galaxies. They focused on the formation of dark matter halos — regions of space where gravity happens to be stronger, and where matter begins to accumulate.

“We believe that dark matter halos are the invisible skeleton of the universe,” Shen explains. “Dark matter structures form first, and then galaxies form within these structures. So, we expect the number of bright galaxies should be proportional to the number of big dark matter halos.”

The team developed an empirical framework for early galaxy formation, which predicts the number, luminosity, and size of galaxies that should form in the early universe, given some measures of “cosmological parameters.” Cosmological parameters are the basic ingredients, or mathematical terms, that describe the evolution of the universe.

Physicists have determined that there are at least six main cosmological parameters, one of which is the Hubble constant — a term that describes the universe’s rate of expansion. Other parameters describe density fluctuations in the primordial soup, immediately after the Big Bang, from which dark matter halos eventually form.

The MIT team reasoned that if early dark energy affects the universe’s early expansion rate, in a way that resolves the Hubble tension, then it could affect the balance of the other cosmological parameters, in a way that might increase the number of bright galaxies that appear at early times. To test their theory, they incorporated a model of early dark energy (the same one that happens to resolve the Hubble tension) into an empirical galaxy formation framework to see how the earliest dark matter structures evolve and give rise to the first galaxies.

“What we show is, the skeletal structure of the early universe is altered in a subtle way where the amplitude of fluctuations goes up, and you get bigger halos, and brighter galaxies that are in place at earlier times, more so than in our more vanilla models,” Naidu says. “It means things were more abundant, and more clustered in the early universe.”

“A priori, I would not have expected the abundance of JWST’s early bright galaxies to have anything to do with early dark energy, but their observation that EDE pushes cosmological parameters in a direction that boosts the early-galaxy abundance is interesting,” says Marc Kamionkowski, professor of theoretical physics at Johns Hopkins University, who was not involved with the study. “I think more work will need to be done to establish a link between early galaxies and EDE, but regardless of how things turn out, it’s a clever — and hopefully ultimately fruitful — thing to try.”

“We demonstrated the potential of early dark energy as a unified solution to the two major issues faced by cosmology. This might be an evidence for its existence if the observational findings of JWST get further consolidated,” Vogelsberger concludes. “In the future, we can incorporate this into large cosmological simulations to see what detailed predictions we get.”

This research was supported, in part, by NASA and the National Science Foundation.

Sulfur has been suggested as a material for lithium-ion batteries because of its low cost and potential to hold more energy than lithium-metal oxides and other materials used in traditional ion-based versions. To make Li-S batteries stable at high temperatures, researchers have previously proposed using a carbonate-based electrolyte to separate the two electrodes (an iron sulfide cathode and a lithium metal-containing anode). However, as the sulfide in the cathode dissolves into the electrolyte, it forms an impenetrable precipitate, causing the cell to quickly lose capacity. Liping Wang and colleagues wondered if they could add a layer between the cathode and electrolyte to reduce this corrosion without reducing functionality and rechargeability.

The team coated iron sulfide cathodes in different polymers and found in initial electrochemical performance tests that polyacrylic acid (PAA) performed best, retaining the electrode’s discharge capacity after 300 charge-discharge cycles. Next, the researchers incorporated a PAA-coated iron sulfide cathode into a prototype battery design, which also included a carbonate-based electrolyte, a lithium metal foil as an ion source, and a graphite-based anode. They produced and then tested both pouch cell and coin cell battery prototypes.

After more than 100 charge-discharge cycles, Wang and colleagues observed no substantial capacity decay in the pouch cell. Additional experiments showed that the pouch cell still worked after being folded and cut in half. The coin cell retained 72% of its capacity after 300 charge-discharge cycles. They next applied the polymer coating to cathodes made from other metals, creating lithium-molybdenum and lithium-vanadium batteries. These cells also had stable capacity over 300 charge-discharge cycles. Overall, the results indicate that coated cathodes could produce not only safer Li-S batteries with long lifespans, but also efficient batteries with other metal sulfides, according to Wang’s team.

The authors acknowledge funding from the National Natural Science Foundation of China; the Natural Science Foundation of Sichuan, China; and the Beijing National Laboratory for Condensed Matter Physics.

In a new study, researchers have determined through both statistical analysis and in experiments that soil pH is a driver of microbial community composition — but that the need to address toxicity released during nitrogen cycling ultimately shapes the final microbial community.

“The physical environment is affecting the nature of microbial interactions, and that affects the assembly of the community,” said co-lead author Karna Gowda, assistant professor of microbiology at The Ohio State University. “People in the field understood these two things must be important at some level, but there wasn’t a lot of evidence for it. We’re adding some specificity and mechanisms to this idea.”

The work helps clarify the microbial underpinnings of global nitrogen cycling and may provide a new way to think about emissions of nitrous oxide, a potent greenhouse gas, Gowda said.

The research was published recently in Nature Microbiology.

Microbes keep soil healthy and productive by recycling nutrients, and are particularly important for converting nitrogen into forms that plants can use. Underground organisms living in the same environment are also highly interconnected, preying on each other, participating in chemical exchanges and providing community benefits.

For this work, Gowda and colleagues used a dataset from a worldwide collection of topsoil samples, sequencing the genomes of microbes present in the samples and analyzing important characteristics of the soil — such as nitrogen and carbon content and pH, a measure of soil’s acidity.

“We wanted to look at trends that were widespread and that would manifest around the planet across very different environments,” Gowda said.

With billions of bacteria present in a sample of soil, the researchers relied on the genetic makeup of microbial communities to determine their functional roles.

The team zeroed in on genes that identified which bacteria were involved in denitrification — converting nitrogen compounds from bioavailable forms into nitrous oxide and dinitrogen gas that’s released in the atmosphere. A bioinformatics analysis showed that soil pH was the most important environmental factor associated with the abundance of these organisms.

To test the statistical finding, the researchers conducted lab enrichment experiments, running a natural microbial community through different conditions of growth.

During denitrification, specific enzymes have roles in the conversion of nitrate into various nitrogen-containing compounds. One of these forms, nitrite, is more toxic in acidic soil (low pH) than it is under neutral conditions with higher pH.

The experiments showed that strains with enzymes called Nar, linked to creating toxic nitrite, and strains with enzymes called Nap, linked to consuming nitrite, fluctuated based on the acidity of the soil.

“We found more of Nar at low pH and less of Nap, and vice versa as the soil pH moved toward neutral,” Gowda said. “So we see two different types of organisms prevalent at acidic versus neutral pH, but we also find that that’s actually not explaining what’s going on. It’s not just the environment that’s determining who’s there — it’s actually the environment plus interactions between more organisms in the community.

“This means that pH is affecting the interaction between organisms in the community in a more or less consistent way — it’s always about the toxicity of nitrite. And this highlights how different bacteria work together to thrive in varying soil pH levels.”

That finding was novel and important, Gowda said. Bacteria and other microorganisms are known to be driven by a will to survive, but they also rely on each other to stay safe — and that cooperation has implications for environmental health, the research suggests.

“While individual fitness effects clearly play a role in defining patterns in many contexts, interactions are likely essential to explaining patterns in a variety of other contexts,” the authors wrote.

Understanding how interactions and the environment affect nitrous oxide emissions could provide new insights into reducing this potent greenhouse gas, Gowda said: Denitrifying bacteria are key sources and sinks of nitrous oxide in agricultural soils. While past studies have focused on the behavior of these nitrous oxide-emitting organisms in different pH conditions, considering their ecological interactions may offer new strategies to lower emissions.

This work was supported by the National Science Foundation, the University of Chicago, the National Institute of General Medical Sciences, a James S. McDonnell Foundation Postdoctoral Fellowship Award, and a Fannie and John Hertz Fellowship Award.

Co-authors include Seppe Kuehn, Kyle Crocker, Kiseok Keith Lee, Milena Chakraverti-Wuerthwein and Zeqian Li of the University of Chicago; Mikhail Tikhonov of Washington University in St. Louis; and Madhav Mani of Northwestern University.