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Reçu aujourd’hui — 2 juillet 20256.5 📰 Sciences English

New open-access journal AI for Science aims to revolutionize scientific discovery

2 juillet 2025 à 10:25
AI for Science journal cover
Intelligent read: the new diamond open-access journal AI for Science will meet the need for high-quality journals dedicated to artificial intelligence (courtesy: IOP Publishing)

Are you in the field of AI for science? Now, you have a new place to share your latest work to the world.  IOP Publishing has partnered with the Songshan Lake Materials Laboratory in China to launch a new diamond” open-access journal to showcase how artificial intelligence (AI) is driving scientific innovationAI for Science (AI4S) will publish high-impact original research, reviews, and perspectives to highlight the transformative applications and impact of AI.

The launch of the interdisciplinary journal AI4S comes as AI technologies become increasingly integral to scientific research from drug discovery to quantum computing and materials science.

AI is one of the most dynamic and rapidly expanding areas of research so much so that in the last five years the topic has expanded by nearly ten times the rate of general scientific output.  

Gian-Marco Rignanese from École Polytechnique de Louvain (EPL) in Belgium, who is the editor-in-chief of Al4S, says he is “very excited” by AI’s transformative potential for science. “It is really disrupting the way research is being performed. AI excels at processing and analyzing large volumes of data quickly and accurately,” he says. “This capability enables researchers to gain insights – or identify patterns – that were previously difficult or impossible to obtain.

Rignanese adds that AI is also accelerating simulations making them “closer to the real world” and large language models and neuro-linguistic programming are changing our way to apprehend the existing literature. “Generative AI holds a lot of promises,” he says.

Rignanese, whose research focuses on investigating and designing advanced materials for electronics, energy storage and energy production in which he uses first-principles simulations and machine learning, says that AI4S “not only targets high standards in terms of quality of the published research” but that it also recognizes the importance of sharing data and software.

The journal recognizes the rapid and multifaceted growth of AI. Notably, in 2025 both the chemistry and physics Nobel prizes went to the science of AI. Research funding is also increasing, with both the US Department of Energy (DOE) and National Science Foundation (NSF) allocating more resources to this field in 2025 than ever before.

In China, AI is emerging as a major priority in which the science community is poised to become a driving force in global development. Reflecting this, AI4S is co-led by editor-in-chief Weihua Wang from the Songshan Lake Materials Laboratory. Songshan Lake Materials Laboratory is a new and leading institute for advanced materials research and innovation that is preparing to focus intensively on AI in the near future.

“Our primary goal with AI for Science is to provide a global forum where scientists can share their cutting-edge research, innovative methodologies, and transformative perspectives,” says Wang The field of AI in scientific research is not only expanding but also evolving at an unprecedented pace, making it vital for professionals to connect and collaborate.”

Wang expressed his optimistic vision for the future of AI in scientific research. “We want AI for Science to be instrumental in creating a more connected and collaborative global community of researchers,” he adds. “Together, we can harness the transformative power of AI to address some of the world’s most pressing scientific challenges and make the field even more impactful.”

Wang notes that the inspiration behind the journal is the potential impact of AI on scientific discovery. “We believe that AI has the power to revolutionize the way research is conducted,” he says. “By providing a space for open dialogue and collaboration, we hope to enable scientists to leverage AI technologies more effectively, ultimately accelerating innovation and improving outcomes across various fields.”

The scope of AI4S is broad yet focused, catering to a wide array of interests within the scientific community. Wang explains that the journal covers various topics. These include: AI algorithms adapted for scientific applications; AI software and toolkits designed specifically for researchers; the importance of AI-ready datasets; and the development of embodied AI systems. These topics aim to bridge the gap between AI technology and its applications across disciplines like materials science, biology, and chemistry.

AI4S is also setting new standards for author experience. Submissions are reviewed by an international editorial board together with the support of a 22-member advisory board composed of leading scientists and engineers. The journal also promises a rapid turnaround in which once accepted, articles are published within 24 hours and assigned a citable digital object identifier (DOI). In addition, from 2025 to 2027, all article publication charges are fully waived, paid for by the Songshan Lake Materials Laboratory.

AI4S joins a growing number of journals focused on machine learning and AI. This includes the IOP’s Machine Learning Series: Machine Learning: Science and Technology; Machine Learning: Engineering; Machine Learning: Earth; and Machine Learning: Health.

“AI is a new approach to science which is really exciting and holds a lot of promises,” adds Rignanese, “so I am convinced that there is room for a journal accompanying this new paradigm.”

For more information or to submit your manuscript, click here.

The post New open-access journal <I>AI for Science</I> aims to revolutionize scientific discovery appeared first on Physics World.

PhD student Ekaterina Shanina wins Early Career Researcher Award for PET phantom study

2 juillet 2025 à 10:00

Ekaterina Shanina, a PhD student at the University of California, Davis, has won the Physics in Medicine & Biology Early Career Researcher Award for her research paper describing a novel brain phantom for positron emission tomography (PET).

Shanina’s study was chosen by Physics in Medicine & Biology’s editorial board as the “best paper” (based on the quality of scientific content and peer review ratings) in the journal’s Early Career Researcher Focus Collection 2024 – a programme established to support and highlight the work of emerging researchers in the medical physics and biomedical engineering community.

“The initiative recognises that early-career researchers often produce cutting-edge, high-impact work but may not yet have widespread visibility,” says Emma Harris, a guest editor on the collection. She explains that while the collection itself showcases a broad range of high-quality work, the award was introduced to further recognise an outstanding contribution from an early-career author – defined this year as someone who completed their PhD in 2018 or later.

“The award serves to highlight exceptional research that stands out for originality, rigour or impact,” says Harris, from the UK’s Institute of Cancer Research and Royal Marsden NHS Trust. “[It will] promote prestige and visibility to the awardee within the international research community, and provide a tangible form of encouragement and recognition that can support academic career progression.”

A new phantom for high-performance PET

In her award winning paper, PICASSO: a universal brain phantom for positron emission tomography based on the activity painting technique, Shanina describes a unique PET phantom called PICASSO and shows how it can be used to model realistic static and dynamic neuroimaging PET studies with excellent quantitative accuracy.

PET imaging offers an invaluable tool for studying the brain, prompting recent interest in developing advanced high-resolution PET scanners dedicated to brain imaging. Such developments create an associated requirement for appropriate imaging phantoms to evaluate and optimize scanner performance. The PICASSO phantom aims to meet these needs.

Ekaterina Shanina with the PICASSO phantom
Device testing Ekaterina Shanina working with the PICASSO painting phantom in the uEXPLORER PET/CT scanner. (Courtesy: Ekaterina Shanina)

“UC Davis has been collaborating with Yale University and United Imaging Healthcare to develop a new high-performance brain PET scanner called the NeuroEXPLORER,” Shanina explains. “This scanner has high spatial resolution, which renders the most commonly used anthropomorphic brain phantom – the Hoffman phantom – unsuitable for evaluating its performance. At the same time, we wanted to explore the activity painting technique to create this unconventional phantom for PET imaging.”

Most physical PET phantoms need to be filled with a radioactive solution, which means that they can only model one type of tracer and making changes to the phantom structure is challenging. Such phantoms also require walls to separate different regions, which interferes with quantitative image evaluation, and designs with complex internal cavities are hard to fill without residual air bubbles.

“Our PICASSO phantom overcomes many of these limitations,” says Shanina.

It works by moving a 22Na point source around within the field-of-view of a PET scanner to “paint” one high-statistics dataset. The motion of the radioactive source is controlled by a robotic arm and contrast levels are defined by computationally sampling the acquired dataset. This approach can efficiently generate phantoms with arbitrary static and dynamic activity distributions in the brain (or other body regions) using a single PET acquisition.

“PICASSO uses a single dataset acquired with a sealed point source to efficiently generate a variety of activity distributions of various complexities and with arbitrarily fine features,” Shanina explains. “There’s no need for cumbersome phantom preparation, there are no cold walls or air bubbles, and the data contain some of the scanner parameters that are difficult to model analytically. We can even use it to model dynamic studies, which is a very challenging task for conventional phantoms.”

Since the paper was published last year, Shanina and colleagues have extended the two-dimensional PICASSO phantom into a 3D version that can generate whole-brain images. “We are also working on an exciting new application for the phantom, using it to model different time-of-flight resolutions of PET scanners,” she says. “To our knowledge, you cannot do this with any other phantoms that are not simulations.”

Shanina tells Physics World that she is “honoured and humbled” to win the Early Career Researcher Award. “I am very happy that this work keeps attracting people’s attention and interest,” she says. “Of course, I don’t do this all by myself. I am very grateful to have Simon Cherry and Jinyi Qi as my advisors supporting and encouraging me on this journey.”

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CAPSTONE™ Celebrates Three Years of Groundbreaking Achievements in Lunar Navigation and Autonomy

2 juillet 2025 à 00:35
terran orbital

IRVINE, Calif. – July 1, 2025 – CAPSTONE™ (Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment), owned and operated by Advanced Space, proudly celebrates its three-year anniversary. Serving as […]

The post CAPSTONE™ Celebrates Three Years of Groundbreaking Achievements in Lunar Navigation and Autonomy appeared first on SpaceNews.

Reçu hier — 1 juillet 20256.5 📰 Sciences English

New mechanism explains behaviour of materials exhibiting giant magnetoresistance

1 juillet 2025 à 19:07

Two distinctive features of materials known as quantum double-exchange ferromagnets are purely due to quantum spin effects and multiorbital physics, with no need for the lattice vibrations previously invoked to explain them. This theoretical result could lead to new insights into these technologically important materials, as it suggests that some of their properties may arise from interactions hitherto regarded as less important.

Quantum double-exchange ferromagnets have interested scientists since the late 1980s, when physicists led by Albert Fert and Peter Grünberg found that their electrical resistance depends strongly on the magnitude of an external magnetic field. This phenomenon is known as giant magnetoresistance (GMR), and its discovery led to an enormous increase in the storage capacity of modern hard-disk drives, which incorporate GMR structures into their magnetic field sensors. It also led, in 2007, to a Nobel Prize for Fert and Grünberg.

Modelling strategies

Despite these successes, however, physicist Jacek Herbrych of the Institute of Theoretical Physics at Wrocław University of Science and Technology in Poland, who led the new research effort, says that these materials remain somewhat mysterious. “They are theoretically complex, and even today, there is no exact solution to fully solve these systems,” he says.

The key question, Herbrych continues, is how Coulomb interactions between many individual electrons lead to the electron spins in these ferromagnets becoming aligned. “Physicists broadly distinguish two mechanisms,” he explains. “For insulating ferromagnets, the Goodenough-Kanamori rules (based on electron shell occupancy and geometrical arguments) can predict spin alignment. For metallic ferromagnets, the double-exchange mechanism is more appropriate.”

In this latter case, Herbrych explains, the electrons’ motion and the alignment of their spins are intrinsically linked, and the electrons often occupy multiple orbitals. This means they need to be modelled in a fundamentally different way.

The approach Herbrych and his colleagues took, which they describe in Rep. Prog. Phys., was conceptually simple, using a basic yet realistic model of interacting electrons to predict the quantum behaviour of electron spins. “In quantum mechanics, ‘simple’ can quickly become complex, however,” Herbrych notes. “Materials in which the double-exchange mechanism dominates typically exhibit multiorbital behaviour, as mentioned. A minimal model must therefore include electron mobility (or ‘itinerancy’), Coulomb interactions and orbital degrees of freedom.”

Two distinctive features

Herbrych and colleagues identified the two-orbital Hubbard-Kanamori model and the Kondo lattice model with interactions as fitting these requirements. They then used these models to explore two distinctive features of quantum double-exchange ferromagnets.

Both features involve magnons, which are collective oscillations of the materials’ spin magnetic moments. In basic “toy” models of ferromagnets, magnons exhibit a well-defined energy-momentum correspondence known as the dispersion relation. Quantum double-exchange ferromagnets, however, experience a phenomenon known as magnon mode softening: at short wavelengths, their magnons become nearly dispersionless, or momentum independent. “This implies that there are fundamental differences between long- and short-distance spin dynamics,” Herbrych says. “Magnons can travel over long distances but appear localized at short scales.”

The second distinctive feature is called magnon damping. This occurs when magnons lose coherence, meaning that the standard picture of spin flips propagating through the material’s lattice breaks down. “It was previously thought that Jahn-Teller phonons (lattice vibrations) were responsible for these features, and that a classical spin model with phonons would do, but our work challenges this view,” says Herbrych. “We show that these phenomena can arise purely from quantum spin effects and multiorbital physics, without requiring lattice vibrations.”

This is, he tells Physics World, “a remarkable result” as it suggests that some experimental features of quantum double-exchange ferromagnets may arise from interactions previously considered secondary.

Limitations and extensions

The researchers’ present work is restricted to one dimension, and they acknowledge that extending it to two or three dimensions will be a challenge. “Still, our approach offers a conceptual framework that can be approximately extended to higher dimensions,” Herbrych says. “The results not only provide insights into the physics of strongly correlated systems, but also into the interplay of competing phases, such as ferromagnetism, orbital order and superconductivity, observed in these materials.”

The post New mechanism explains behaviour of materials exhibiting giant magnetoresistance appeared first on Physics World.

Heisenberg (not) in Helgoland: where two paths diverge

1 juillet 2025 à 16:30

Helgoland

5 June: I am somewhat relieved Professor Born accepted my request for leave at short notice. The hay fever in Göttingen seems worse this year than last when I returned from Copenhagen. Even when not coughing, sneezing or stemming tears from my eyes, I am barely able to string two thoughts together. My thinking jumps from place to place with no sense of continuity, place or direction. I leave for Helgoland immediately.

6 June: The journey has been long and less than pleasant, but I have arrived. Seeing my puffed-up face and eyes swollen shut, the landlady of the guesthouse said, “Oh my, what a state! Who did this to you? I have a quiet room on the second floor where you may recover from your fight. Peace and rest is what you need.” I did not correct her observation for she meant well.

7 June: Sunday has been a day of rest and recovery. This treeless island already offers better relief than my usual attempts at medication. The air is fresh and I am drawn to wander in the sunshine rather than hide from it.

9 June: The sea air has brought with it a new perspective. While we cannot deny that the assortment of observations, equations and ideas we have support a quantum view, it is generous to call their sum a theory. They are parts in loose association. While we can observe the intensity of hydrogen’s spectral lines, we cannot observe all that we believe we need to know in order to explain their intensity. My island perspective, being so close to the stuff of water, is that perhaps it is our belief that is at fault? What if we can let those unobservables remain that way?

10 June: Yes, this thinking has momentum, although I am uncertain where it will lead. Perhaps we must give up the demands of our lingering Newtonian worldview and give ourselves over more fully to the mathematics.

There is a before and an after: we know where the electron is on either side of a transition, and that should be sufficient. We need not trouble ourselves with the story in between – the mathematics is untroubled, it is only our previously held beliefs that cause difficulty!

14 June: I am a little distressed by possible asymmetries in what I have formulated. I am not yet ready to abandon causality and conservation, as Bohr and colleagues so boldly – and unsuccessfully – attempted last year.

15 June: I wandered out in the middle of the night and headed to the south shore where I climbed a rock to sit in thought. I have found no contradiction within this theory or in its relation to other truths – energy is conserved! Within the consistency and coherence of the mathematics, I also see beauty and a wealth of possibility. There is a lingering asymmetry in the operations, but I made peace with that as I watched the sun rise and observed the waves. Wave on wave may be commutative, but wave on shore is not. Such noncommutativity seems also to be the case with the tabular system of numbers I have used.

16 June: I leave for Hamburg. I wish to share these insights with Pauli ahead of my return to Göttingen. Before sharing my insights with Professor Born, I need for Wolfgang to confirm what I have unearthed is not wrong and that this theory is not some sea madness.

Göttingen

5 June: I am somewhat aggrieved that Professor Born did not grant my request for leave. Admittedly, the notice was short, but the hay fever is most wretched. I am barely able to string two thoughts together, let alone a theory for electron transition. The problem of hydrogen’s spectral lines eludes me, as does any coherence during much of the day or night. The lushness of Göttingen’s parks and gardens is a curse in summer. If I am to make progress on this problem of physics, I must first address this problem of my own biology.

6 June: Chemistry is today’s pursuit. I have secured medication in a greater dose than before.

7 June: Empirically, I appear to have determined that a more generous ingestion of cocaine is not the solution to my hay fever problem. I shall instead switch to increasing my intake of aspirin.

11 June: I am feeling most sorry, both for myself and the state of our discipline. It is as though my own ills are entangled with physics as a whole. There is little certainty or clarity, only contradictions and incompleteness. Whether at the scale of the atom or the galaxy, our understanding contradicts our intuition and our progress out of this darkness is pitiful.

Even Professor Einstein’s magnificent general theory of relativity has its difficulties. Without a fix that lacks any theoretical origin, it predicts an expanding universe! There are even  solutions that permitted dark stars whose gravity would be so large that nothing could escape! We are mired in questions and nonsense, all the while I am little more than coughs, sneezes and reddened eyes. What I might generously call my mind is barely deserving of the name.

I am consoled, at least, that in mathematics the story is not the same. Russell and Whitehead have shown that mathematics is complete and consistent – although I know of no one who has managed to read the whole proof. This result offers a firm bedrock I am sure mathematicians will continue to celebrate a hundred years from now.

15 June: I was en route to the department this morning when I entirely lost my bearings after taking a wrong turn from my usual route. Imagine knowing where I was going but not knowing where I was!

Just last week I had the opposite experience. My landlady accosted me just in front of the Friedhofskapelle Stadtfriedhof. I was as surprised to see her as we was to see me. “Good day, Professor Heisenberg.” I long ago stopped reminding her that I was no professor, merely a Privatdozent. She means well. “Where are you heading?” And do you know, I had no idea! How I wish, though, that Born had let me travel to Helgoland.

16 June: As I walk – and sneeze – into the university this morning, I am caused to wonder from where answers to our quantum troubles might emerge. Bohr has great insight, so will it be from Copenhagen that an interpretation will appear? Or perhaps it will from Cambridge — Paul Dirac’s thinking is particularly fresh.

For now, I wish an end to summer and the fog it has brought to my thinking, yet I also wonder whether we are asking more of nature than she is prepared to share with us. Perhaps it is our dearly held beliefs that hold us back. Perhaps nature and mathematics do not share those beliefs. Perhaps. There is an uncertainty within me that I find hard
to articulate.

  • To hear the author read an extract from the diaries and reflect on the power of “flash fiction”, check out the Physics World Stories podcast.

This article forms part of Physics World‘s contribution to the 2025 International Year of Quantum Science and Technology (IYQ), which aims to raise global awareness of quantum physics and its applications.

Stayed tuned to Physics World and our international partners throughout the year for more coverage of the IYQ.

Find out more on our quantum channel.

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Coulomb liquid emerges from five electrons in a semiconductor

1 juillet 2025 à 14:01

As few as five electrons in a semiconductor can exhibit collective behaviour, forming a “Coulomb liquid”, according to researchers in Europe. This extends the study of correlated systems to electron plasmas, and could lead to the study of other exotic phases of matter.

A conventional plasma is a hot, ionized gas of free electrons and positive ions. However, the conduction band of a semiconductor can be considered a one-component plasma. “The effect of the positive charges, as they are locked into the lattice, can be modelled as a uniform background of positive charge,” says team member Vyacheslavs Kashcheyevs of the University of Latvia in Riga. In conventional electronics and semiconductor physics, the conduction band is modelled as a 2D Fermi gas of non-interacting particles, with the Coulomb interaction between the electrons neglected.

The new work focused on electron–electron correlations in the conduction band of gallium arsenide at millikelvin temperatures. The team created a Y-shaped junction. Electrons emitted from a quantum dot were steered through the device by an externally-generated surface acoustic wave (SAW) potential. Part-way through, the path divided, and each electron could either go left or right. The number taking each path was measured by separate quantum dots. The researchers are uncertain, and the model is agnostic, about the extent to which the randomness of left or right arose from quantum mechanics.

When no more than one electron was loaded into each potential minimum, each electron’s choice was random, and the number of electrons counted at each detector after multiple trials could be modelled by a binomial distribution. However, when the researchers tuned the apparatus such that each minimum contained multiple electrons, they found changes in the distribution, with groups of particles less likely to travel to the same detector than would be naïvely expected.

Calculating “cumulants”

The researchers quantified the changes in the distributions using probability theory, calculating “cumulants” of the distributions. “We not only have a cumulant of order two, which would say that two particles are repulsing,” says Hermann Sellier of Institut Néel in Grenoble, France, who led the experimental research. “We have a cumulant of order four for four particles or five for five particles, showing that each particle is talking to all the other particles of the droplet. That’s much stronger and something that has not been measured before.”

This shows, say the researchers, that the 2D electron gas condenses into a strongly correlated Coulomb liquid. This a phase of matter seen in quark–gluon plasma, which is created by the high-energy collision of heavy ions, but never previously identified in electronic matter.

“It’s not like you have atoms which, below a certain temperature, go from the gas phase to the liquid phase because of an attractive interaction,” explains Sellier. “We say that the correlated behaviour is like that of a liquid, but a very special liquid made of repulsive interactions. You push on the right, it pushes on the left.” This is possible only at low temperatures because heating increases the entropy to the point where the correlated state of matter is disfavoured.

The team now wants to look at larger systems approaching the macroscopic limit. They believe similar systems could potentially be used to study many-body physics with other, exotic particles such as anyons – quasiparticles that have properties intermediate to bosons and fermions. Potential technological applications include cold atom quantum simulation.

Considerable interest

Ravi Rau of Louisiana State University in the US says, “It is an interesting method, novel to me, of controlling electron droplets and being able to measure correlations of two, three and up to a maximum of five-particles so far, and addressing the general question of the transition in few-body systems to the statistical limit from explicit dynamics when the number of particles is small”. He adds, “This study, such a system, and the results presented will of course be of considerable interest.”

Rau does however, note that very similar results were achieved in the past in studies of electron collisions with cold atoms and molecules. “[That technique] went under the name of COLTRIMS (cold target recoil-ion momentum spectroscopy) allowed measuring multiple differential cross sections and studying electron–electron correlations in atoms,” he says. “It was the exact analogue of this [work], except that instead of an artificially created and controlled droplet cluster, the electrons were naturally inside the atom.”

The researchers acknowledge the similarity, and thank Rau for bringing the previous work to their attention. However, Kashcheyevs argues that the new work has a generality that allows it to tackle new problems, finding the scaling law that connects the properties of individual electrons to the properties of incompressible Coulomb plasma. “Applying our method at lower temperatures in the future can probe the quantum regime of the phase diagram of this electronic fluid, which is known to support exotic quasiparticles impossible in the 3D vacuum of the Standard Model,” he says.

The research is described in Nature.

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Liberatech Space to offer custom Earth-observation products for commodity, energy and environmental monitoring

1 juillet 2025 à 00:30

SAN FRANCISCO – While working in finance years ago, Yasunori Yamazaki traveled to mines to conduct due diligence. Later, as Axelspace chief business officer and Astroscale head of brand management, he considered how satellites could simplify the task. As a result, one of the first products being developed by his new company Singapore-based Liberatech Space, […]

The post Liberatech Space to offer custom Earth-observation products for commodity, energy and environmental monitoring appeared first on SpaceNews.

Cambrian Works Announces Upcoming GigRouter Launch to the International Space Station

30 juin 2025 à 23:53
cambrian works logo

LOS GATOS, CA– Cambrian Works, an innovator in technological connections between Earth and space, is proud to announce their GigRouter flight unit is ready for launch aboard Aegis Aerospace’s MISSE-21 […]

The post Cambrian Works Announces Upcoming GigRouter Launch to the International Space Station appeared first on SpaceNews.

Reçu avant avant-hier6.5 📰 Sciences English

Space is hard. There is no excuse for pretending it’s easy.

30 juin 2025 à 15:00
Starship ship

The headlines in the space industry over the past month have delivered a sobering reminder: space is not forgiving, and certainly not friendly to overpromising entrepreneurs. From iSpace’s second failed lunar landing attempt (making them 0 for 2) to SpaceX’s ongoing Starship test flight setbacks — amid a backdrop of exploding prototypes and shifting goalposts […]

The post Space is hard. There is no excuse for pretending it’s easy. appeared first on SpaceNews.

X-rays reveal a cosmic filament

30 juin 2025 à 14:00

New observations support the idea that hot, diffuse threads of gas called cosmic filaments connect clusters of galaxies across the cosmos. That is the conclusion of Konstantinos Migkas at Leiden University and colleagues who say that their study strengthens the idea that much of the normal matter in the universe resides in these structures.

About 5% of the universe’s mass–energy content appears to be baryonic matter – the familiar nuclei and particles that make up atoms and molecules. The rest is believed to be dark energy and dark matter, which are both hypothetical entities. Although they know what baryonic matter is, astronomers have a poor understanding of where much of it is distributed in the universe.

Combining the Standard Model of cosmology with the rigid constraints enforced by observations of cosmic microwave background radiation tells us that structures including stars, black holes, and gas clouds account for around 60% of baryonic matter in the universe. This leaves 40% of baryonic matter unaccounted for.

Previously, cosmologists have argued that this discrepancy could point to a fundamental error in the Standard Model. Recently, however, a growing body of evidence suggests that this matter could be found in vast yet elusive structures, hidden deep within intergalactic space.

On a WHIM

“Large-scale structure simulations of the universe tell us this material should reside within long strings of gas called ‘cosmic filaments’, which connect clusters of galaxies,” Migkas explains. “These missing baryons should be found in the so-called ‘warm-hot intergalactic medium’ (WHIM).”

Despite being extremely sparse, models also predict that the WHIM should be extremely hot – primarily heated by shock waves produced as matter collapses into the large-scale cosmic web, as well as by phenomena including active galactic nuclei and mergers between galaxy clusters. As a result, these cosmic filaments should be emitting a faint yet detectable X-ray signal.

On top of this, the Standard Model places tight theoretical constraints on several physical properties of the WHIM – including its density, temperature, and composition. If X-rays are indeed being emitted by cosmic filaments, these properties should be encoded in their energies, intensities, and frequency spectra – providing astronomers with a clear target in their search for the elusive structures.

These X-ray signals have so far evaded detection because they are extremely faint compared to powerful X-ray signals such as those coming from supermassive black holes

To overcome this, researchers combined data from two of the world’s most advanced X-ray observatories. One is the Suzaku satellite, which was jointly operated by JAXA and NASA and was very good at detecting very faint signals. The other is the ESA’s XMM-Newton, which is very good at observing powerful X-ray signals.

Eliminating black holes

“Combining the two instruments, we carefully and appropriately eliminated the contaminating signal of the black holes throughout our filament,” Migkas explains. “This enabled us to isolate the signal of WHIM and measure its density and temperature for the very first time with such accuracy.”

For an observational target, Migkas’ team searched for cosmic filaments in the Shapley supercluster. This vast structure around 650 million light-years from the Milky Way contains one of the highest concentrations of galaxies in the known universe.

With the combined abilities of Suzaku and XMM-Newton, the researchers detected an X-ray signal indicating the presence of a filament – consistent with predictions of the Standard Model. As they expected, this intergalactic material was extremely hot and sparse: boasting temperatures close to 10 million Kelvin, while containing just around 10 electrons per cubic metre.

“We also found that on average, the filament is around 40 times denser than the average density of the universe – which is pretty empty in general – and around 1000 times less dense than the cores of the four-galaxy cluster it connects,” Migkas describes. Despite having gone undetected so far, this filament also carries a total mass around 10 times that of the Milky Way – making it a vast reservoir of previously hidden matter.

“For the very first time, our work confirms the validity of the predictions of the Standard Model of cosmology regarding the properties of a big part of the missing baryons,” Migkas concludes.

The research is described in Astronomy and Astrophysics.

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