It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Tuesday, October 03, 2023
Accounting for oxygen in modeling coastal ecosystems
Driven by climate change and pollution, the decline of oxygen levels in oceans is altering biogeochemical cycles, threatening marine plants, animals and ecosystems. But how accurately are we projecting the fate of marine life? If models of marine ecosystems are to truly inform management — especially of coastal areas — they must account for the variation in oxygen levels across time and space, KAUST researchers say.
“Our study provides a perspective on the monitoring of oxygen decline in the ocean from a different angle,” says principal investigator Daniele Daffonchio. “Oceanic systems have a natural mechanism for regulating oxygen dissolution by balancing oxygen-consuming (respiration) and oxygen-producing (photosynthesis) processes.”[1]
Current models fail to project oxygen dynamics of coastal ecosystems that have an abundance of organisms that photosynthesize, says marine scientist Marco Fusi, who led the study with Folco Giomi from the University of Padova, Italy. Examples include seagrass meadows, mangrove forests and coral reefs. “It’s a very different dynamic from what’s seen in unproductive parts of the ocean in some cases called the ‘blue desert,’” he says.
In an initial observation of crabs in a mangrove forest, Fusi found they could survive in waters reaching over 40 degrees, well above their known thermal threshold. The waters were “oxygen-supersaturated,” a state in which more oxygen was dissolved in the water than would be through equilibrium with the atmosphere. This extra oxygen production due to warmer temperatures was helping the crustaceans cope.
The researchers also discuss fluctuations in the Venice Lagoon, once considered one of the most oxygen-depleted “dead zones” in the Adriatic Sea. The lagoon hosts a complex mosaic of ecosystems that include seagrasses and salt marshes colonized by microalgae and cyanobacteria. While dissolved oxygen was low at night, the lagoon reached nearly 300 percent saturation during the day.
Data from coral reefs in the Red Sea — formerly regarded a low oxygen zone due to high temperatures — shows a similar pattern. “The marine species in these areas are accustomed to living in a rollercoaster of oxygen levels,” says Fusi.
The team advises that conservation management should be based not on linear models focusing on average values of dissolved oxygen, but on a more complex mathematical model that incorporates the variation.
“Predictions of biodiversity loss in the Red Sea from two decades ago indicated that 90 percent of biodiversity would have been lost by now. That hasn’t happened yet. This could mean two things: that the modeling had been too simplistic and that species living in productive marine ecosystems have high capacity for adaptation,” says Fusi. “Our hope is that our study boosts the discussion on how we could better incorporate fluctuations into models and of new methods to study the resilience of marine species.”
LEIBNIZ-INSTITUT FÜR LEBENSMITTEL-SYSTEMBIOLOGIE AN DER TU MÜNCHEN
IMAGE: PHOTO OF COMMON HOP (HUMULUS LUPULUS) ON WHITE BAKGROUND.view more
CREDIT: GISELA OLIAS / LEIBNIZ-LSB@TUM
Hop-derived constituents not only increase shelf-life and bitterness of beer, but can also significantly influence aroma. An important hop odorant is linalool, which has a floral and citrus-like scent. Under the leadership of the Leibniz Institute for Food Systems Biology at the Technical University of Munich, a team of scientists has now disproved a roughly 20-year-old assumption about this odorant. The new study contributes to a better understanding of changes in beer bouquet during the brewing process and beer aging.
Two molecular variants of the odorant linalool are found in hops and beer: the enantiomers (R)- and (S)-linalool. Both molecules consist of the same number and type of atoms, and show the same connectivity. Nevertheless, they have a different spatial structure and differ like an image from its mirror image. This "small" but nevertheless crucial difference is also reflected in different odor intensities of the molecules.
In addition, it has long been known that beer aroma changes during the brewing process and storage because, among other things, part of the (R)-linalool predominant in hops is converted to (S)-linalool. Previously, based on a 1999 paper, researchers assumed that the odor threshold concentration of (R)-linalool is about a factor of 80 lower than that of (S)-linalool. Put simply, they assumed that (R)-linalool has a much stronger influence on beer aroma than its mirror-image counterpart. However, reliable data on the odor thresholds of both substances were lacking.
Preparative method optimized
To close this knowledge gap and enable more precise predictions of changes in beer aroma, the team led by brewing and beverage technologist Klaas Reglitz and food chemist Martin Steinhaus from the Leibniz Institute first optimized a preparative method. In close cooperation with the Research Center Weihenstephan for Brewing and Food Quality, the researchers thus succeeded for the first time in isolating enantiomerically pure (S)-linalool.
Having the pure substance available in sufficient quantities was an indispensable prerequisite for determining the specific odor threshold concentrations of the two odorant variants in water and unhopped beer using a trained sensory panel. This was essential because only (R)-linalool is commercially available as a pure substance.
As the team showed, the thresholds of (R)- and (S)-linalool in water were 0.82 and 8.3 micrograms per kilogram, respectively. In unhopped beer, the team determined thresholds of 6.5 micrograms per kilogram for (R)-linalool and 53 micrograms per kilogram for (S)-linalool.
Influence of (R)-linalool overestimated
"Our results thus confirm the previously postulated higher odor potency of (R)-linalool. However, they also refute the previous assumption that the odor threshold concentrations of the two enantiomers differ extremely. Instead, the study shows that the difference is only about eight to tenfold," says Martin Steinhaus, head of Section I and the Food Metabolome Chemistry Research Group at the Leibniz Institute.
First author Klaas Reglitz adds, "The conversion of (R)- to (S)-linalool thus does not have as great an influence on beer aroma as has long been assumed. Thanks to our study, we now better understand how and why the aroma changes during storage."
Linalool Linalool is an important constituent in many essential oils, often as a major component. It is found in various spice plants such as coriander, star anise, hops, nutmeg, ginger, basil and many others. Linalool is used both as a component of essential oils and as a pure compound for flavoring purposes.
Hops The common hop (Humulus lupulus) is mainly used for beer production. For brewing, the cones of the female hop plants are used. In 2022, the hop acreage in Germany was approximately 20,600 hectares, which is roughly one-third of the world's acreage. Germany is thus one of the leading hop producers and plays a significant role in global exports. With an export volume of 26,648 tons, Germany tops the list of hop exporting countries. At the same time, Germany is also one of the most important destination countries for the international hop trade. Source:https://de.statista.com/
LEIBNIZ-INSTITUT FÜR LEBENSMITTEL-SYSTEMBIOLOGIE AN DER TU MÜNCHEN
The photo shows a full glass of beer with a brown beer bottle next to it.
CREDIT
Gisela Olias / Leibniz-LSB@TUM
Information about the Institute:
The Leibniz Institute for Food Systems Biology at the Technical University of Munich (Leibniz-LSB@TUM) comprises a new, unique research profile at the interface of Food Chemistry & Biology, Chemosensors & Technology, and Bioinformatics & Machine Learning. As this profile has grown far beyond the previous core discipline of classical food chemistry, the institute spearheads the development of food systems biology. It aims to develop new approaches for the sustainable production of sufficient quantities of food whose biologically active effector molecule profiles are geared to health and nutritional needs, but also to the sensory preferences of consumers. To do so, the institute explores the complex networks of sensorically relevant effector molecules along the entire food production chain with a focus on making their effects systemically understandable and predictable in the long term.
The Leibniz-LSB@TUM is a member of the Leibniz Association (https://www.leibniz-gemeinschaft.de/en/), which connects 97 independent research institutions. Their orientation ranges from the natural sciences, engineering, and environmental sciences through economics, spatial and social sciences to the humanities. Leibniz Institutes devote themselves to social, economic, and ecological issues. They conduct knowledge-oriented and application-oriented research, also in the overlapping Leibniz research networks, are or maintain scientific infrastructures and offer research-based services. The Leibniz Association focuses on knowledge transfer, especially with the Leibniz Research Museums. It advises and informs politics, science, business, and the public. Leibniz institutions maintain close cooperation with universities - among others, in the form of the Leibniz Science Campuses, industry, and other partners in Germany and abroad. They are subject to a transparent and independent review process. Due to their national significance, the federal government and the federal states jointly fund the institutes of the Leibniz Association. The Leibniz Institutes employ around 21,000 people, including almost 12,000 scientists. The entire budget of all the institutes is more than two billion euros.
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IMAGE: CAPE BARREN GOOSE (PHOTO COURTESY D COLOMBELLI-NEGREL, FLINDERS UNIVERSITY)view more
CREDIT: S KLEINDORFER (KONRAD LORENZ RESEARCH CENTRE FOR BEHAVIOUR AND COGNITION, UNIVERSITY OF VIENNA)
Facial recognition software used to study the social behaviour of individual Greylag Geese in Europe will soon be used to monitor one of the rarest geese in the world, the Cape Barren Goose in South Australia.
The technology was used to assess how each bird responds to images of themselves, other flock mates or partners and researchers from the University of Vienna and Flinders University say it could be used by other scientists or in citizen science apps around the world to monitor and record endangered wildlife or even to promote the welfare of animals in captivity.
Flinders BirdLab leaders Professor Sonia Kleindorfer and Dr Diane Colombelli-Négrel, worked on the software with support from the University of Vienna, University of Veterinary Medicine in Austria and the Konrad Lorenz Research Centre for Behaviour and Cognition.
The program tested each goose face with lifesize 2D images of members of the Greylag Goose flock, originally started by the founding father of animal behaviour, Austrian scientist Konrad Lorenz in the 1950s.
With 97% accuracy, each goose face could be correctly assigned within a photo library containing 6000 possible matches, researchers say in a new article in Journal of Ornithology.
“Next the team placed life-sized photos in a grassy field to see whether geese behave differently to each image – which they do,” says Professor Kleindorfer, who founded Flinders University’s BirdLab 20 years ago and now directs the Konrad Lorenz Research Centre, a core facility at the University of Vienna in Austria.
“The geese approached the photo of their partner more quickly, gave friendly contactcalls and fed for longer. In contrast, when they saw a picture of themselves – a goose they had never seen before – they hissed and took longer to approach food, if they fed at all.”
The latest findings into visual cues of individuality not only gives insights into the birds’ social structure but illustrate how the software to monitor individual faces or body patterns can be monitored using photographs collected in the field – for animal numbers and movements – in conservation efforts.
“Animal welfare could also be enhanced through the use of photographs in captivity,” says Flinders University’s Dr Colombelli-Négrel, from the College of Science and Engineering.
"For example, a photo might reduce the sense of isolation in a social species held in captivity, or serve as a ‘soft introduction’ before a new animal is introduced into an enclosure, although care should be given to avoid photos of a deceased relative, ally or dominant animal in the group.
“Perhaps captive individuals in group-living species express reduced anxiety when exposed to a photograph of an unknown and smaller non-specific,” she adds.
Zoologist Konrad Lorenz, who was awarded the Nobel Prize in Physiology or Medicine with Nikolas Tinbergen and Karl von Frisch in 1973, used the behaviour of the Greylag Goose to found the discipline of animal behaviour.
Playing Tetris for fifteen minutes can prevent psychological trauma in mothers after a difficult birth. These are the conclusions of a large-scale study conducted at CHUV and HUG and published in Molecular Psychiatry. The study's findings pave the way for a routine intervention to prevent the development of post-traumatic stress symptoms linked to childbirth.
An international team at Lausanne University (UNIL) and Lausanne University Hospital (CHUV) shows that a therapeutic activity comprising fifteen minutes of playing the video game Tetris can prevent the development of symptoms of posttraumatic stress linked to childbirth - or "CB-PTSD". The large-scale study led by the team of Antje Horsch, associate professor at UNIL’s Faculty of Biology and Medicine and research consultant at the Department Mother-Infant-Child of CHUV, involved 146 women. Of these women, half played Tetris and half carried out a placebo activity in the first six hours following their emergency caesarean section. The results show that the Tetris group had significantly fewer symptoms of PTSD, and this for up to six months after childbirth.
By engaging the 'visuospatial' region of the brain, the area that deals with vision and orientation in space, Tetris can interfere with the memory consolidation of traumatic images. Such images play a critical role in the development of PTSD. As memory consolidation takes place within few hours, playing Tetris shortly after a difficult event may thereby prevent the development of PTSD. The team around Antje Horsch is the first to prove the preventive effectiveness of such an intervention for traumatic childbirth.
With one in five women negatively impacted after an emergency caesarean section, PTSD linked to childbirth is a common mental health disorder. It manifests itself in the form of flashbacks and nightmares, irritability, difficulty sleeping, and hypervigilance about the baby. These symptoms can seriously disrupt daily life and have repercussions for the whole family. At present, prevention of childbirth-related PTSD is challenging due to the lack of scientifically validated treatments.
The results of Antje Horsch's team may have a significant impact not only on the prevention of PTSD after traumatic childbirth, but also after other types of trauma. "We are very enthusiastic because the activity was carried out under the supervision of the midwives and nurses in the maternity units, showing that it can be integrated into routine care. What's more, it's short, inexpensive, and accessible to anyone, regardless of their native language. It therefore has real clinical potential", explain Drs. Camille Deforges and Vania Sandoz, the study's first authors.
Funded by the Swiss National Science Foundation, the study was conducted in a rigorous manner using a randomised, controlled, double-blind protocol, reinforcing the reliability and robustness of the results. It thereby represents a major advance in mental health care after difficult childbirth and, more generally, after any traumatic event.
Publication
Deforges, C.*, Sandoz, V.*, Noël, Y., Avignon, V., Desseauve, D., Bourdin, J.,Vial, Y., Ayers, S., Holmes, E.A., Epiney, M. & Horsch, A. (2023). Single-session visuospatial task procedure to prevent childbirth-related posttraumatic stress disorder: a multicentre double-blind randomised controlled trial. Molecular Psychiatry. DOI: 10.1038/s41380-023-02275-w
IMAGE: THE GAS CONVERSION PROCESS BY AN ELECTRODE-BASED ENZYMATIC REACTION. THE ENZYME EXTRACTED FROM THE MICROBE, BOUND TO A GRAPHITE ELECTRODE, CAN BE EMPLOYED TO CONVERT THE GREENHOUSE GAS CARBON DIOXIDE TO FORMATE, A MOLECULE THAT CAN BE USED AS SAFE ENERGY STORAGE OR AS A BASIS FOR CHEMICAL SYNTHESIS. THE TWO MOLECULES ARE SHOWN AS BALLS AND STICKS (CARBON ATOMS IN GREY, OXYGEN ATOMS IN RED). THE STRUCTURE OF THE PROTEIN FROM THE METHANOGEN METHANOTHERMOBACTER WOLFEII IS SHOWN AS A LIGHT BLUE SURFACE TO ILLUSTRATE THE ENZYME. THE ENERGY REQUIRED BY THE ELECTRODE CAN ORIGINATE FROM RENEWABLE ENERGY SOURCES.view more
CREDIT: O. LEMAIRE, M. BELHAMRI AND T. WAGNER/ MAX PLANCK INSTITUTE FOR MARINE MICROBIOLOGY
Seeking microorganisms that efficiently capture the greenhouse gas CO2 “The enzymes employed by the microorganisms represent a fantastic playground for scientists as they allow highly specific reactions at fast rates”, says Tristan Wagner, head of the Max Planck Research Group Microbial Metabolism at the Max Planck Institute for Marine Microbiology (MPIMM). Some of these enzymes have an interesting way of capturing CO2: They transform it into formate, a stable and safe compound that can be used to store energy or to synthesize various molecules for industrial or pharmaceutical purposes. One example is Methermicoccus shengliensis, a methanogen (a microbe producing methane) isolated from an oilfield and growing at 50 °C. It has been cultivated and studied over the past years by Julia Kurth and Cornelia Welte at Radboud University in the Netherlands. At the Max Planck Institute for Marine Microbiology, Olivier Lemaire, Mélissa Belhamri and Tristan Wagner dissected the microbe to find its CO2-capturing enzyme and measure how fast and efficiently it can transform CO2.
A CO2-converting enzyme with great potential The Max Planck-scientists undertook the challenging task to isolate the microbial enzyme. “Since we knew that such enzymes are sensitive to oxygen, we had to work inside an anaerobic tent devoid of ambient air to separate it from the other proteins – quite complicated, but we succeeded”, says Olivier Lemaire. Once isolated, the scientists characterized the enzyme’s properties. They showed that it efficiently generates formate from CO2 but performs the reverse reaction at very slow rates and poor yield. “Similar enzymes belonging to the family of formate dehydrogenases are well known to operate in both directions, but we showed that the enzyme from Methermicoccus shengliensis is nearly unidirectional and could not efficiently convert the formate back into CO2”, reports Mélissa Belhamri. “We were quite thrilled by this phenomenon, occurring only in the absence of oxygen”, she adds. “Since the formate generated from CO2-fixation cannot be transformed back and therefore accumulates, such a system would be a highly interesting candidate for CO2-capture, especially if we could branch it on an electrode”, Tristan Wagner points out. The advantage of that: With the enzyme naturally or chemically attached to an electrode, the “energy” required to capture the CO2 will be directly delivered by the electrode, without electric current loss or the need for expensive or toxic chemical compounds as relays. Consequently, the enzyme-bound electrodes are efficient and attractive systems for gas conversion procedures. Thus, the purified enzyme was sent to the University of Geneva to set up an electrode-based CO2-capture system.
Electricity-based gas conversion Selmihan Sahin and Ross Milton from the University of Geneva are specialists in electrochemistry. They use electrodes connected to electric current to perform chemical reactions. The electrode-based formate generation from CO2 often requires polluting and rare metals, and that is why they tried to replace these metals with the enzyme extracted in the group of Tristan Wagner at the MPIMM. The procedure of enzyme binding on an electrode is not always as efficient as expected, but the enzyme from Wagner’s research group has specific characteristics that could facilitate the process. The scientists from Switzerland managed to fix the enzyme on a graphite electrode, where it performed the gas conversion. The measured rates were comparable to those obtained with classic formate dehydrogenases. “The strength of this biological system coupled to the electrode lies in its efficiency in transferring the electrons from the electricity towards CO2 transformation”, highlights Lemaire. Sahin and Milton also confirmed that the system performs the reverse reaction poorly, as previously observed in the reaction tube. Consequently, the modified electrode continuously converted the greenhouse gas to formate without any detectable side-products generated or electric current loss.
Towards a new solution for atmospheric CO2 utilization The collaborative work provides a new molecular tool to the scientific community: An enzyme converting CO2 by transferring electricity with high efficiency. Renewable green energy (e.g., wind or solar) could provide electricity to the electrode-based system that would turn CO2 into formate, a molecule directly usable for applications or to store energy. “Before us, no one ever tried to study an enzyme from such a methanogen for an electrode-based gas conversion”, says Tristan Wagner. “Yet, methanogens are natural outstanding gas converters”. As powerful as they could be, employing enzymes for large-scale processes would also require similar-scale enzyme production systems, a considerable investment. Therefore, while the discovered strategy could, in theory, significantly improve CO2 transformation, a deep knowledge of the enzyme mechanism is necessary before its application, and the team of researchers will now have to dissect in depth the molecular secrets of the reaction.
Bioelectrocatalytic CO2 Reduction by Mo-Dependent Formylmethanofuran Dehydrogenase
Genetic study of citrus fruits suggests they originated in southern China
Fruit characteristics of the orange subfamily and differences in fruit citric acid levels among Citrus-related genera, wild Citrus and domesticated Citrus. a, Fruits from Citrus (1–18) and Citrus-related genera (19–30). 1, C. reticulata; 2, C. maxima; 3, C. medica; 4, C. polyandra (formerly Clymenia polyandra); 5, C. sinensis; 6, Citrus aurantium; 7, C. hongheensis; 8, Citrus paradisi; 9, Citrus limon; 10, C. indica; 11, C. linwuensis; 12, C. hystrix; 13, C. glauca (formerly E. glauca); 14, C. australasica (formerly M. australasica); 15, C. hindsii (formerly Fortunella hindsii); 16, C. ichangensis; 17, C. mangshanensis; 18, C. trifoliata (formerly Poncirus trifoliata); 19 and 20, A. buxifolia; 21 and 22, Citropsis gilletiana; 23, Aegle marmelos; 24 and 25, Murraya paniculata; 26–28, Clausena lansium; 29, Glycosmis pentaphylla; 30, Bergera koenigii. Individual pieces of fruit from different pictures were collected and are shown together. Scale bars, 1 cm. b, Citric acid content of fruit pulp from Citrus-related genera and Citrus species. The numbers of independent samples used in this analysis are indicated and data are presented as the mean ± s.d. Credit: Nature Genetics (2023). DOI: 10.1038/s41588-023-01516-6
A team of horticulturists, genealogists and germplasm specialists affiliated with multiple institutions in China, working with two colleagues from the U.S. and one from Australia, has found evidence that suggests citrus fruits originated in what is now southern China. In their study, reported in the journal Nature Genetics, the group built a family tree of citrus fruits using a variety of techniques.
Citrus fruits tend to grow in warm or tropical climates and come in many varieties, many of which are human cultivated. But up until now, it has not been clear where citrus fruits first appeared. Some had suggested they might have originated in certain parts of Australia, the foothills of the Himalayas, or southern areas in China. In this new effort, the researchers sought to find a more conclusive answer.
The researchers conducted a genetic study of 314 citrus or citrus-related plants. They also conducted fieldwork, venturing to places where citrus plants were thought to exist but were unverified—this allowed them to find and classify a large number of wild species. The team then used data from all of their combined sources to create a family tree for citrus fruits. They found that the species C. trifoliata was the oldest, at approximately 8 million years old—today, it grows in southern parts of China. That suggested that southern China is the birthplace of citrus fruit.
The researchers suggest that citrus fruit species growing in China could have made their way to what is now India when the Asian tectonic plate collided with the Indian tectonic plate approximately 25 million years ago. From there, they could have spread all the way to lands surrounding the Mediterranean Sea.
As part of their work, the research team also found the gene responsible for controlling the amount of citric acid produced by a given fruit—PH4. They found that when activated, it fires up a proton pump that promotes the production of citric acid, and by extension, the degree of tartness.
More information: Yue Huang et al, Pangenome analysis provides insight into the evolution of the orange subfamily and a key gene for citric acid accumulation in citrus fruits, Nature Genetics (2023). DOI: 10.1038/s41588-023-01516-6
This artist’s impression shows a Population III star that is 300 times more massive than our Sun exploding as a pair-instability supernova. Credit: NOIRLab/NSF/AURA/J. da Silva/Spaceengine
If you take a universe worth of hydrogen and helium, and let it stew for about 13 billion years, you get us. We are the descendants of the primeval elements. We are the cast-off dust of the first stars, and many generations of stars after that. So our search for the first stars of the cosmos is a search for our own history. While we haven't captured the light of those first stars, some of their direct children may be in our own galaxy.
The first stars were massive. Without any heavier elements to weigh them down, they needed to be about 300 times that of our sun in order to trigger nuclear fusion in their core. Because of their size, they went through their fusion cycles rather quickly and lived very short lives.
But the supernova explosions signaling their deaths scattered heavier elements such as carbon and iron from which new stars formed. Large second-generation stars also died as supernovae and scattered even more heavy elements. As a result, each generation of stars contained more and more of these elements. In astronomy lingo, we say each generation has a higher metallicity.
Of course, which generation a star is in can be fuzzy. Clearly, the very first stars, forming entirely out of primordial hydrogen and helium are first-generation stars, and stars forming entirely out of the remnants of the first generations are true second-generation stars. But stars form at all different sizes, so it's quite likely that some massive second-generation stars became supernova before some of the smaller first-generation stars.
Many early stars could have formed from mostly first-generation material with a touch of second-generation dust, while others formed mostly from second-generation stars with a sprinkling of first-generation heritage. Stars like our sun are likely a mix of material from multiple generations.
The distribution of stars in our galaxy. Credit: NASA, ESA, and A. Feild [STScI]
For modern stars, rather than trying to determine their generation, we categorize them into populations based on their metallicity. A star's metallicity is taken as the ratio of iron to helium [Fe/He] on a logarithmic scale. Population I stars have an [Fe/He] of at least -1, meaning they have 10% of the sun's iron ratio or more. Population II stars have an [Fe/He] of less than -1. The third category, Population III, is reserved for true first-generation stars.
In the Milky Way galaxy, most of the stars in the galactic plane are population I stars like the sun. They formed much later in the history of our galaxy, and are younger with more metals. Older population II stars are generally found in the halo surrounding our galaxy, or in the old globular clusters that orbit the Milky Way. That makes sense since older stars have had more time to drift out of the galactic plane. Given the evolution of our galaxy, it's quite likely that some of the population II stars in our halo are truly second-generation stars. But how can we distinguish them from other old stars?
That's the goal of a new study published on the arXiv preprint server. It looks at both observations of distant quasars and simulations of population III stars to determine the metallicity of truly second-generation stars. The authors found that while second-generation stars would be rare in the Milky Way halo, some could be lurking there. The key to identifying them is not their abundance of iron relative to helium, [Fe/He], but rather the ratios of carbon and magnesium to iron, [C/Fe] and [Mg/Fe].
Identifying second-generation halo stars. Credit: Vanni, et al
Carbon is formed in stars as part of the CNO cycle, which is the second-level fusion cycle after hydrogen burning. Magnesium is a product of a 3-stage fusion of carbon with helium. Many first-generation stars exploded as high-powered supernovae, but some exploded with lower energy. These low-energy supernovae would cast off elements such as carbon and magnesium, but not much iron. So, stars with an exceptionally high [C/Fe] ratio likely formed from the remnant material of a single first-generation star. The lower the [C/Fe] ratio, the more likely a population II star formed from first and second-generation stars.
So it seems the key is to look for halo stars with [C/Fe] > 2.5. We haven't found any such stars yet, but as more sky surveys come online it is likely only a matter of time. We will still have to search the most distant galaxies to find a first-generation star, but we may soon find one of their children much closer to home.
More information: Irene Vanni et al, Characterising the true descendants of the first stars, arXiv (2023). DOI: 10.48550/arxiv.2309.07958
