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How the ‘heart and lungs’ of a galaxy extend its life
Galaxies avoid an early death because they have a “heart and lungs” which effectively regulate their “breathing” and prevent them growing out of control, a new study suggests.
That’s according to a new study published in the Monthly Notices of the Royal Astronomical Society, which investigates one of the great mysteries of the Universe — why galaxies are not as large as astronomers would expect.
Something appears to be stifling their enormous potential by limiting the amount of gas they absorb to convert into stars, meaning that instead of endlessly growing, something inside resists what was thought to be the inevitable pull of gravity.
Now, astrophysicists at the University of Kent think they may have uncovered the secret. They suggest that galaxies could in fact control the rate at which they grow through how they “breathe.”
In their analogy, the researchers compared the supermassive black hole at the centre of a galaxy to its heart and the two bi-polar supersonic jets of gas and radiation they emit to airways feeding a pair of lungs.
Pulses from the black hole — or “heart” — can lead to jet shock fronts oscillating back and forth along both jet axes, much like the thoracic diaphragm in the human body moves up and down inside a chest cavity to inflate and deflate both lungs.
This can result in jet energy being transmitted widely into the surrounding medium, just as we breathe out warm air, resulting in slowing galaxy gas-accretion and growth.
PhD student Carl Richards came up with the theory after creating new, never-before-tried simulations to investigate the role supersonic jets might play in inhibiting galaxy growth.
These involved allowing the black hole “heart” to pulse and the jets to be at high pressure — much like a form of hypertension, if extending the comparison to the human body.
This caused the jets to “act like bellows,” he said, by sending out sound waves “like ripples on a pond surface.”
The phenomena is similar to the terrestrial equivalent of sound and shock waves being produced when opening a bottle of champagne, the screech of a car, rocket exhausts and the puncture of pressurised enclosures.
“We realised that there would have to be some means for the jets to support the body — the galaxy’s surrounding ambient gas — and that is what we discovered in our computer simulations,” Richards said.
“The unexpected behaviour was revealed when we analysed the computer simulations of high pressure and allowed the heart to pulse.
“This sent a stream of pulses into the high-pressure jets, causing them to change shape as a result of the bellows-like action of the oscillating jet shock fronts.”
These overpressured jets effectively expanded “like air-filled lungs,” the researchers said.
In doing so, they transmitted sound waves into the surrounding galaxy in the form of a series of pressure ripples, which were then shown to suppress the galaxy’s growth.
There is some evidence of ripples in extra-galactic media, such as those observed in the nearby Perseus galaxy cluster associated with enormous hot gas bubbles, which are believed to be examples of sound waves.
These ripples were already thought to be responsible for sustaining the ambient environment surrounding a galaxy, although a mechanism to generate them was missing.
Conventional cosmological simulations are therefore unable to account for the flows of gas into galaxies, leading to one of the great mysteries of the Universe, so it relies on the highly-active black hole at a galaxy’s heart to provide some resistance.
“To do this is not easy, however, and we have constraints on the type of pulsation, the size of the black hole and the quality of the lungs,” said co-author Professor Michael Smith.
“Breathing too fast or too slow will not provide the life-giving tremors needed to maintain the galaxy medium and, at the same time, keep the heart supplied with fuel.”
The researchers concluded that a galaxy’s lifespan can be extended with the help of its “heart and lungs,” where the supermassive black hole engine at its core helps inhibit growth by limiting the amount of gas collapsing into stars from an early stage.
This, they say, has helped create the galaxies we see today.
Without such a mechanism, galaxies would have exhausted their fuel by now and fizzled out, as some do in the form of “red and dead” or “zombie” galaxies.
The paper ‘Simulations of Pulsed Overpressure Jets: Formation of Bellows and Ripples in Galactic Environments’, Carl Richards and Michael Smith, has been published in Monthly Notices of the Royal Astronomical Society.
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Early dark energy could resolve cosmology’s two biggest puzzles
A new study by MIT physicists proposes that a mysterious force known as early dark energy could solve two of the biggest puzzles in cosmology and fill in some major gaps in our understanding of how the early universe evolved.
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.
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Plant-derived secondary organic aerosols can act as mediators of plant-plant interactions
A new study published in Science reveals that plant-derived secondary organic aerosols (SOAs) can act as mediators of plant-plant interactions. This research was conducted through the cooperation of chemical ecologists, plant ecophysiologists and atmospheric physicists at the University of Eastern Finland.
The study showed that Scots pine seedlings, when damaged by large pine weevils, release VOCs that activate defences in nearby plants of the same species. Interestingly, the biological activity persisted after VOCs were oxidized to form SOAs. The results indicated that the elemental composition and quantity of SOAs likely determines their biological functions.
“A key novelty of the study is the finding that plants adopt subtly different defence strategies when receiving signals as VOCs or as SOAs, yet they exhibit similar degrees of resistance to herbivore feeding,” said Professor James Blande, head of the Environmental Ecology Research Group. This observation opens up the possibility that plants have sophisticated sensing systems that enable them to tailor their defences to information derived from different types of chemical cue.
“Considering the formation rate of SOAs from their precursor VOCs, their longer lifetime compared to VOCs, and the atmospheric air mass transport, we expect that the ecologically effective distance for interactions mediated by SOAs is longer than that for plant interactions mediated by VOCs,” said Professor Annele Virtanen, head of the Aerosol Physics Research Group. This could be interpreted as plants being able to detect cues representing close versus distant threats from herbivores.
The study is expected to open up a whole new complex research area to environmental ecologists and their collaborators, which could lead to new insights on the chemical cues structuring interactions between plants.
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Folded or cut, this lithium-sulfur battery keeps going
Most rechargeable batteries that power portable devices, such as toys, handheld vacuums and e-bikes, use lithium-ion technology. But these batteries can have short lifetimes and may catch fire when damaged. To address stability and safety issues, researchers reporting in ACS Energy Letters have designed a lithium-sulfur (Li-S) battery that features an improved iron sulfide cathode. One prototype remains highly stable over 300 charge-discharge cycles, and another provides power even after being folded or cut.
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.
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