TOP SCEINCE
Planet-forming disks around very low-mass stars are different
Planets form in disks of gas and dust, orbiting young stars. The MIRI Mid-INfrared Disk Survey (MINDS), led by Thomas Henning from the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, aims to establish a representative disk sample. By exploring their chemistry and physical properties with MIRI (Mid-Infrared Instrument) on board the James Webb Space Telescope (JWST), the collaboration links those disks to the properties of planets potentially forming there. In a new study, a team of researchers explored the vicinity of a very low-mass star of 0.11 solar masses (known as ISO-ChaI 147), whose results appear in the journal Science.
“These observations are not possible from Earth because the relevant gas emissions are absorbed by its atmosphere,” explained lead author Aditya Arabhavi of the University of Groningen in the Netherlands. “Previously, we could only identify acetylene (C2H2) emission from this object. However, JWST’s higher sensitivity and the spectral resolution of its instruments allowed us to detect weak emission from less abundant molecules.”
The MINDS collaboration found gas at temperatures around 300 Kelvin (ca. 30 degrees Celsius), strongly enriched with carbon-bearing molecules but lacking oxygen-rich species. “This is profoundly different from the composition we see in disks around solar-type stars, where oxygen-bearing molecules such as water and carbon dioxide dominate,” added team member Inga Kamp, University of Groningen.
One striking example of an oxygen-rich disk is the one of PDS 70, where the MINDS program recently found large amounts of water vapour. Considering earlier observations, astronomers deduce that disks around very low-mass stars evolve differently than those around more massive stars such as the Sun, with potential implications for finding rocky planets with Earth-like characteristics there. Since the environments in such disks set the conditions in which new planets form, any such planet may be rocky but quite unlike Earth in other aspects.
What does it mean for rocky planets orbiting very low-mass stars?
The amount of material and its distribution across those disks limits the number and sizes of planets the disk can supply with the necessary material. Consequently, observations indicate that rocky planets with sizes similar to Earth form more efficiently than Jupiter-like gas giants in the disks around very low-mass stars, the most common stars in the Universe. As a result, very low-mass stars host the majority of terrestrial planets by far.
“Many primary atmospheres of those planets will probably be dominated by hydrocarbon compounds and not so much by oxygen-rich gases such as water and carbon dioxide,” Thomas Henning pointed out. “We showed in an earlier study that the transport of carbon-rich gas into the zone where terrestrial planets usually form happens faster and is more efficient in those disks than the ones of more massive stars.”
Although it seems clear that disks around very low-mass stars contain more carbon than oxygen, the mechanism for this imbalance is still unknown. The disk composition is the result of either carbon enrichment or the reduction of oxygen. If the carbon is enriched, the cause is probably solid particles in the disk, whose carbon is vaporised and released into the gaseous component of the disk. The dust grains, stripped of their original carbon, eventually form rocky planetary bodies. Those planets would be carbon-poor, as is Earth. Still, carbon-based chemistry would likely dominate at least their primary atmospheres provided by disk gas. Therefore, very low-mass stars may not offer the best environments for finding planets akin to Earth.
JWST discovers a wealth of organic molecules
To identify the disk gases, the team used MIRI’s spectrograph to decompose the infrared radiation received from the disk into signatures of small wavelength ranges — similar to sunlight being split into a rainbow. This way, the team isolated a wealth of individual signatures attributed to various molecules.
As a result, the observed disk contains the richest hydrocarbon chemistry seen to date in a protoplanetary disk, consisting of 13 carbon-bearing molecules up to benzene (C6H6). They include the first extrasolar ethane (C2H6) detection, the largest fully-saturated hydrocarbon detected outside the Solar System. The team also successfully detected ethylene (C2H4), propyne (C3H4), and the methyl radical CH3 for the first time in a protoplanetary disk. In contrast, the data contained no hint of water or carbon monoxide in the disk.
Sharpening the view of disks around very low-mass stars
Next, the science team intends to expand their study to a larger sample of such disks around very low-mass stars to develop their understanding of how common such exotic carbon-rich terrestrial planet-forming regions are. “Expanding our study will also allow us to understand better how these molecules can form,” Thomas Henning explained. “Several features in the data are also still unidentified, warranting additional spectroscopy to interpret our observations fully.”
Background information
The study was funded in the framework of the ERC Advanced Grant “Origins — From Planet-Forming Disks to Giant Planets” (Grant ID: 832428, PI: Thomas Henning, DOI: 10.3030/832428).
The MPIA scientists involved in this study are Thomas Henning, Matthias Samland, Giulia Perotti, Jeroen Bouwman, Silvia Scheithauer, Riccardo Franceschi, Jürgen Schreiber, and Kamber Schwartz.
Other researchers include Aditya Arabhavi (University of Groningen, the Netherlands [Groningen]), Inga Kamp (Groningen), Ewine van Dishoeck (Leiden University, the Netherlands and Max Planck Institute for Extraterrestrial Physics, Garching, Germany), Valentin Christiaens (University of Liege, Belgium), and Agnes Perrin (Laboratoire de Météorologie Dynamique/IPSL CNRS, Palaiseau, France).
The MIRI consortium consists of the ESA member states Belgium, Denmark, France, Germany, Ireland, the Netherlands, Spain, Sweden, Switzerland, and the United Kingdom. The national science organisations fund the consortium’s work — in Germany, the Max Planck Society (MPG) and the German Aerospace Center (DLR). The participating German institutions are the Max Planck Institute for Astronomy in Heidelberg, the University of Cologne, and Hensoldt AG in Oberkochen, formerly Carl Zeiss Optronics.
JWST is the world’s premier space science observatory. It is an international program led by NASA jointly with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).
TOP SCEINCE
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.
TOP SCEINCE
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.
TOP SCEINCE
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.
-
Solar Energy3 years ago
DLR testing the use of molten salt in a solar power plant in Portugal
-
world news1 year ago
Gulf, France aid Gaza, Russia evacuates citizens
-
Camera1 year ago
DJI Air 3 vs. Mini 4 Pro: which compact drone is best?
-
Camera4 years ago
Charles ‘Chuck’ Geschke, co-founder of Adobe and inventor of the PDF, dies at 81
-
world news1 year ago
Strong majority of Americans support Israel-Hamas hostage deal
-
Camera1 year ago
Sony a9 III: what you need to know
-
Solar Energy1 year ago
Glencore eyes options on battery recycling project
-
Indian Defense3 years ago
Israeli Radar Company Signs MoU To Cooperate With India’s Alpha Design Technologies