Using the Atacama Large Millimeter/submillimeter Array (ALMA), an international team of astronomers, with the participation of ICCUB-IEEC researcher Gemma Busquet, has mapped a magnetic highway driving a powerful galactic wind into the nearby galaxy merger of Arp 220, revealing for the first time that its fast, molecular outflows are strongly magnetized and likely helping to drive metals, dust, and cosmic rays into the space around the galaxy. By watching how tiny dust grains and gas molecules line up with these fields, researchers have drawn the most detailed magnetic map yet of Arp 220’s buried, star‑forming cores and their outflows. The result is a new way to see how gravity, starbirth, black holes, and magnetic forces all work together in a chaotic cosmic environment. 
 

Arp 220 is an ultraluminous infrared galaxy (ULIRG) made up of two spiral galaxies in the final stages of merging. Because Arp 220 is the nearest galaxy of its kind, it serves as a powerful time machine: what happens here today likely mirrors what happened in the first generations of massive, dusty galaxies more than 10 billion years ago.
 

“We used ALMA to map the orientation and strength of magnetic fields in the twin galaxies,” shared Enrique Lopez-Rodriguez, the lead author of this research, and an Associate Professor with the University of South Carolina. “This revealed previously unseen details about Arp 220’s dust-enshrouded cores and molecular outflows, including the first detection of a polarized CO(3–2) molecular line emission,”  adds Josep Miquel Girart,  the lead in the observational work, and a researcher at the Institut de Ciències de l'Espai. This emission traced the galactic outflow in the external galaxy, showing that the outflowing gas itself carries a well-ordered magnetic field.
 

Observations of the west nucleus of Arp 220 revealed a nearly vertical magnetic field that runs alongside a bipolar molecular outflow moving at up to roughly 500 kilometers per second, driving a powerful, magnetic superhighway out of the galaxy. Galaxy mergers and starbursts are known to launch powerful winds that can shut down, or regulate, star formation by removing gas. However, these new results show that magnetic fields are a crucial, previously unknown driver in the force of these winds.

The team obtained full-polarization ALMA observations at 870 microns (Band 7), measuring both dust continuum polarization and CO(3–2) line polarization at a resolution of about 0.24 arcseconds (≈96 parsecs), fine enough to separate the two compact nuclei and their outflows. The dust polarization traces magnetically aligned grains in the cold, dense interstellar medium, while the Goldreich–Kylafis effect imprints linear polarization on the CO(3–2) emission line in the presence of anisotropic radiation and magnetic fields, together providing a three-dimensional view of the field geometry.

By combining the polarization geometry with measurements of gas mass, turbulence, and outflow speed, the authors applied and refined versions of the Davis–Chandrasekhar–Fermi method to estimate the magnetic field strengths in the blue- and redshifted outflow lobes. In the eastern nucleus, ALMA revealed a spiral-like magnetic pattern threading a compact, dust-enshrouded disk and arm, suggesting that ordered spiral fields can survive deep into the merger stage.

A highly polarized highway of dust between the two nuclei, with polarization fractions of about 3–5 percent, traces a magnetized ridge that may be funneling material and magnetic flux between the merging cores. Adds Lopez-Rodriguez, “When Arp 220 is observed as a whole, it’s one of the best places in the Universe for astronomers to study how gravity, star formation, and powerful winds work together with strong magnetic fields to reshape a galaxy and seed its surroundings with magnetized gas and dust.”

The team estimates magnetic field strengths of roughly 1–10 milligauss in the molecular outflows—hundreds to thousands of times stronger than the average magnetic field in the Milky Way’s disk—implying that compressed and turbulence-amplified fields help steer material into the circumgalactic medium. Because Arp 220 is the closest analog to the extreme, dusty star-forming galaxies in the early Universe, these results suggest that strong, organized magnetic fields may be common in high-redshift starbursts and could regulate star formation and feedback across cosmic time.

These ALMA observations show that magnetic fields are a major engine in driving material out of galaxies like Arp 220. The strong, ordered fields in its galactic winds act like invisible guardrails, guiding metals, dust, and cosmic rays into the vast cocoon of gas surrounding the system. That material will eventually help build and enrich future generations of stars and galaxies. As astronomers turn ALMA and future telescopes toward ever more distant galaxies, they expect to find similar magnetic superhighways at work across the cosmos. Studies like this transform Arp 220 from a single spectacular merger into a crucial blueprint for understanding how galaxies grow, shut down, and recycle their material over cosmic time—shaping the Universe we see today.

About NRAO
The National Radio Astronomy Observatory (NRAO) is a facility of the U.S. National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

About ALMA
The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.
 

Researchers from the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) and the Institute of Space Studies of Catalonia (IEEC), in collaboration with the Instituto de Astrofísica de Canarias (IAC), have led the largest observational study ever conducted on massive runaway stars including rotation and binarity in our Galaxy. This work, recently published in Astronomy & Astrophysics, sheds light on how these stellar “fugitives” are launched into space and what their properties reveal about their intriguing origins.

Runaway stars are stars that travel through space at unusually high speeds, moving away from the sites where they were born. The way that  massive runaway stars acquired their high speeds have long puzzled astronomers that considered two scenarios: a powerful push when a companion explodes as a supernova in a binary system, or a gravitational ejection during close encounters in dense and young star clusters. However, the relative contribution of these scenarios to understand massive runaway stars were not well constrained in the Milky Way.

Using data from Gaia, a space observatory from the European Space Agency (ESA), and high-quality spectroscopic information from the IACOB project, the team analyzed 214 O-type stars, which are the most massive and luminous stellar objects in the Galaxy. They combined measurements of rotation speed and binarity (whether the star is single or part of a binary system) for the largest sample of Galactic O-type runaway stars to understand their origins. 

The results show that most runaway stars rotate slowly, but those that rotate faster are more likely linked to supernova explosions in binary systems. The fastest-moving stars tend to be single, suggesting they were ejected from young clusters through gravitational interactions. Interestingly, they found that there are almost no runaway stars that move fast and rotate fast, highlighting potential distinct formation pathways. The researchers also identified twelve runaway binary systems, including three known high-mass X-ray binaries (systems that host neutron stars or black holes), and three other binaries that are promising candidates to host black holes.

Massive runaway stars are not just curiosities, they influence the evolution of galaxies. By escaping their birthplaces, they spread heavy elements and radiation across the interstellar medium, shaping future generations of stars and planets. Understanding their origins helps refine models of stellar evolution, supernova explosions, and even the formation of gravitational wave sources. In this context, this work serves as a benchmark for the next generation of massive binary stellar evolution models and cluster dynamical studies.

“This is the most comprehensive observational study of its kind in the Milky Way,” says Mar Carretero-Castrillo, lead author of the study who is now based at the European Southern Observatory. “By combining rotation and binarity information, we provide the community with unprecedented constraints on how these stellar runaways form.”

Future data releases from Gaia and ongoing spectroscopic surveys will allow astronomers to expand these samples and trace the past trajectories of runaway stars, linking them to their birth places. This will help confirm which formation mechanisms dominate and uncover new candidates for exotic systems like high-energy binaries hosting neutron stars or black hole companions.
 

Reference:

https://ui.adsabs.harvard.edu/abs/2025arXiv251021577C/abstract

A&A: https://www.aanda.org/10.1051/0004-6361/202556646

DOI: https://doi.org/10.1051/0004-6361/202556646

Contact:

Mar Carretero-Castrillo mcarrete@eso.org

An international team of scientists led by the Institute of Cosmos Sciences of the University of Barcelona and the Institute of Space Studies of Catalonia (ICCUB-IEEC) have introduced REGALADE, an unprecedented all-sky catalog that brings together nearly 80 million galaxies. This achievement, now published in the prestigious journal Astronomy & Astrophysics (A&A), marks a turning point for astronomy, enabling researchers to explore cosmic events with a level of precision never seen before.

When a telescope detects a sudden phenomenon such as a supernova or the merger of two black holes or neutron stars, astronomers need to know where to look and how far away the event occurred. That requires identifying the galaxy hosting the event. Until now, existing catalogs were incomplete beyond about 300 million light-years, leaving large gaps in our map of the nearby Universe. REGALADE fills those gaps by combining data from major surveys and cleaning it using data from the Gaia mission to remove stars mistakenly classified as galaxies. The result is a high-purity, high-completeness catalog that includes accurate distances and size measurements for all galaxies, and stellar masses for most. 

“REGALADE began as a user experience problem: astronomers relied on many popular catalogs, but each one covered only part of the sky or lacked key information,” explains Hugo Tranin, ICCUB researcher and lead author of the study. “By merging data from 14 widely used catalogs and deep imaging surveys, we now have a single, unified place to look for galaxy distances and properties. This drastically simplifies the daily work of astronomers and allows our team to retrieve distances for more than 75% of the transients reported worldwide every day.” The team has also released an interactive sky viewer (https://blackpearl.blackgem.org/regalade.php), where the public can explore the REGALADE catalog and navigate millions of galaxies in just a few clicks.

The scale and depth of REGALADE are extraordinary. It covers the entire sky and reaches out to more than four billion light-years, mapping about 10% of the volume of the observable Universe. This completeness means astronomers can now identify many more host galaxies for all types of cosmic events, from infrared to X-rays, and significantly improve strategies for gravitational-wave follow-up. According to Nadia Blagorodnova, ICCUB-IEEC researcher and co-author, “Observatories like the Vera Rubin Observatory will detect millions of cosmic events every night. REGALADE ensures we can identify their host galaxies quickly and accurately, enabling rapid classification of rare transients such as luminous red novae, stellar mergers that our team actively studies, and opening the door to the discovery of entirely new types of celestial phenomena.”

The study was led by Hugo Tranin, researcher at the Institute of Cosmos Sciences of the University of Barcelona (ICCUB), with the participation of ICCUB-IEEC researchers Nadejda Blagorodnova, Marco A. Gómez-Muñoz and Maxime Wavasseur. Their work combines expertise in time-domain astronomy, galaxy surveys and multi-messenger astrophysics, positioning the ICCUB team at the forefront of efforts to build comprehensive resources for the next generation of observatories.

Reference: 

Tranin, H., Blagorodnova, N., Gómez‑Muñoz, M. A., Wavasseur, M., Groot, P. J., Landsberg, L., Stoppa, F., Bloemen, S., Vreeswijk, P. M., Pieterse, D. L. A., van Roestel, J., Scaringi, S., Faris, S.,et al. (2025). A catalog to unite them all: REGALADE, a revised galaxy compilation for the advanced detector era. [Article]. Astronomy & Astrophysics. https://doi.org/10.1051/0004-6361/202556896

A new study led by researchers at the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) and the Centre national de la recherche scientifique (CNRS) offers fresh insights into how galaxies like our Milky Way form and evolve and why their stars show surprising chemical patterns.

Published in Monthly Notices of the Royal Astronomical Society, the research explores the origins of a puzzling feature in the Milky Way: the presence of two distinct groups of stars with different chemical compositions, known as the “chemical bimodality.”

What is chemical bimodality?

When scientists study stars near the Sun, they find two main types based on their chemical makeup, specifically, the amounts of iron (Fe) and magnesium (Mg) they contain. These two groups form separate “sequences” in a chemical diagram, even though they overlap in metallicity (how rich they are in heavy elements like iron). This has long puzzled astronomers.

The new study uses advanced computer simulations (called the Auriga simulations) to recreate the formation of galaxies like the Milky Way in a virtual universe. By analyzing 30 simulated galaxies, the team looked for clues about how these chemical sequences form.

Understanding the chemical history of the Milky Way helps scientists piece together how our Galaxy, and others like it, came to be. This includes our sister galaxy, Andromeda, in which no bimodality has yet been detected. It also provides clues about the conditions in the early universe and the role of cosmic gas flows and galaxy mergers.

“This study shows that the Milky Way’s chemical structure is not a universal blueprint,” says lead author Matthew D. A. Orkney, researcher at ICCUB and the Institut d’Estudis Espacials de Catalunya (IEEC). “Galaxies can follow different paths to reach similar outcomes, and that diversity is key to understanding galaxy evolution.”

Key findings
 

The study reveals that galaxies like the Milky Way can develop two distinct chemical sequences through various mechanisms. In some cases, this bimodality arises from bursts of star formation followed by periods of little activity, while in others it results from changes in the inflow of gas from the galaxy’s surroundings. Contrary to previous assumptions, the collision with a smaller galaxy known as Gaia-Sausage-Enceladus (GSE) is not a necessary condition for this chemical pattern to emerge. Instead, the simulations show that metal-poor gas from the circumgalactic medium (CGM) plays a crucial role in forming the second sequence of stars. Moreover, the shape of these chemical sequences is closely linked to the galaxy’s star formation history.

As new telescopes like the James Webb Space Telescope (JWST) and upcoming missions such as PLATO and Chronos provide more detailed data on stars and galaxies, researchers will be able to test these findings and refine our picture of the cosmos.

“This study predicts that other galaxies should exhibit a diversity of chemical sequences. This will soon be probed in the era of 30m telescopes where such studies in external galaxies will become routine. Ultimately, these will also help us further refine the physical evolutionary path of our own Milky Way,” adds Chervin Laporte (ICCUB-IEEC, CNRS-Observatoire de Paris and Kavli IPMU). 

Participating Institutions

This research has been led by researchers from the Institute of Cosmos Sciences of the University of Barcelona (ICCUB), the Institute of Space Studies of Catalonia (IEEC) and the CNRS with the collaboration of scientists from Liverpool John Moores University and the Max-Planck-Institut für Astrophysik.

 

Reference:

Orkney, M. D. A., et al. (2025). The Milky Way in context: The formation of galactic discs and chemical sequences from a cosmological perspective. Monthly Notices of the Royal Astronomical Society. https://doi.org/10.1093/mnras/staf1551

Of the many open questions that puzzle physicists today, there is one, most relevant to cosmologists that crystallises into a single number: the Hubble constant H0, which stands for the ratio between how far a cosmic object is from us and how fast it moves away from us due to the accelerating expansion of the Universe. The puzzle comes from the statistically significant discrepancy between the values of H0 obtained through different measurement strategies: the traditional method, based on the observation of cosmic objects such as Cepheid variable stars and supernovae, or a more indirect approach that uses the cosmic microwave background as the starting point for inferring H0. If this 'Hubble tension' is real, that is, if the differing values of H0 aren't caused by yet-to-be-found systematic uncertainties in the measurements, this calls for a profound rethinking of what we believe we know about the evolution and composition of the Universe.

In a paper just published in the journal Astronomy & Astrophysics, the TDCOSMO collaboration documents their latest effort in pursuing an alternative path to the precise measurement of the Hubble constant. The team’s results further support the Hubble tension between late- and early-Universe measurements of H0. “To me the lensing time delays is pivotal in the tension resolution as it is fully independent of any other method and as it does not involve complicated calibrations” says Frédéric Courbin, ICREA researcher at the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) and the Institute of Space Studies of Catalonia (IEEC). 
 

The TDCOSMO collaboration uses a technique known as time-delay cosmography to infer the value of the Hubble constant. In the paper, the team applies this method to a sample of cosmic probes known as strongly lensed quasars. A quasar is a distant, extremely bright object produced by an accretion disk of gas and dust falling into a supermassive black hole at the centre of a galaxy. 
 

When a massive object, such as a galaxy, stands between an observer and a quasar, an effect known as gravitational lensing produces multiple images of the quasar. This is because the so-called lens galaxy, also referred to as the deflector, acts a bit like an optical lens placed on the path of a light beam: it warps space and, as a result, bends and magnifies the light coming from a background object. In the case of a quasar, the light's deflection produces bright, distorted lensed images around the lens galaxy (see header image in this article).
 

Crucially, the signature of gravitational lensing on an observed quasar is not just spatial, but temporal too. If the intensity of the radiation emitted by a quasar varies over time, the light rays coming from multiple images of one lensed quasar reach us with temporal delays. Time-delay cosmography allows researchers to measure what is known as time-delay distance. Provided the gravitational potential of the lens galaxy is sufficiently well known, scientists can infer H₀ from the time-delay distance and the light's redshift caused by the expanding Universe.

To obtain the new value of H₀, the TDCOSMO team used previously collected as well as new data on eight strongly lensed quasars and took advantage of improved analysis methods. For six out of eight lens galaxies, the data related to stellar kinematics were made accessible by the NIRSpec spectrograph on the James Webb Space Telescope. Stellar kinematics data refer to the motion of stars in a galaxy: they're especially important to address a major source of error when determining H₀ with time-delay cosmography. Other data were collected with the Multi Unit Spectroscopic Explorer (MUSE) spectrograph at the Very Large Telescope of the European Southern Observatory (ESO) in Chile and with the Keck Cosmic Web Imager (KCWI) at the Keck Observatory in Hawaii.

The latest findings from the TDCOSMO collaboration underscore the critical role of international research networks and sustained investment in science. Thanks to the visionary support of the Swiss National Science Foundation (SNSF), researchers were able to collect two decades of time-delay measurements of lensed quasars using the Swiss Leonhard Euler Telescope at ESO. This long-term effort was further strengthened by European funding through the ERC Advanced Grant COSMICLENS (PI: Frédéric Courbin).

Highlighting the significance of this research, the European Commission has recently awarded a €12 million Synergy Grant to tackle the Hubble tension through the RedH0T project, co-led by researchers Licia Verde (ICREA-ICCUB) and Frédéric Courbin.

Reference:

Birrer, S. et al. TDCOSMO 2025: Cosmological constraints from strong lensing time delays. Astronomy & Astrophysics.

https://doi.org/10.1051/0004-6361/202555801

Available at https://www.aanda.org/component/article?access=doi&doi=10.1051/0004-6361/202555801

Based on the press release from ETH Zurich.

An international team led by researchers from the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) has received a Synergy Grant from the European Research Council to resolve the Hubble tension, one of the major challenges in modern cosmology and a source of disagreement when measuring the expansion rate of the universe. The project, called RedH0T, will receive more than €12 million in funding (around €6 million allocated to the UB).

Licia Verde, ICREA researcher and Scientific Director of ICCUB, is the coordinator of RedH0T. This project’s principal investigators also include Frédéric Courbin, ICREA researcher at ICCUB and the Institute of Space Studies of Catalonia (IEEC); Julien Lesgourques, from Aachen University (Germany) and Adam Riess, from Johns Hopkins University (United States), winner of the 2011 Nobel Prize in Physics for demonstrating that the expansion of the universe is accelerating.

“RedH0T aims to address one of the challenges that cosmology has faced for years: Is the significant discrepancy between measurements of the Hubble constant (H₀) caused by observational errors or limitations of the current cosmological model? If the latter is true, we would be facing one of the most significant discoveries of the 21^st century, with profound implications for fundamental physics,” says Licia Verde.

The researcher adds: “RedH0T is expected to improve on all current measures of H₀ with cross-checks and internal consistency, thereby producing robust results that can guide cosmologists in revising the current paradigm.”

The project also stands out for its innovative approach, which is pioneering in cosmology. RedH0T introduces the red-teaming method, inspired by cybersecurity. “In the field of cybersecurity, ethical hackers conduct simulated, non-destructive cyberattacks to test the effectiveness of systems. In our case, we want each methodology for measuring the Hubble constant to be analysed by three different teams, which allows each method to be validated or questioned with maximum transparency and rigour, promoting scientific consensus,” says Fred Courbin.

This collaborative work will be carried out by a blue team, made up of experts who will develop the methodology; a red team, composed of specialists who will challenge assumptions and look for vulnerabilities; and a white team, with neutral figures who will oversee the process.

International institutions in pursuit of an ambitious goal

In addition to the University of Barcelona (project coordinator), Aachen University and Johns Hopkins University, the Alma Mater Studiorum - University of Bologna, The Chancellor Masters and Scholars of the University of Oxford and the University of Chicago are also participating in the project. The team from the UB’s Institute of Cosmos Sciences is completed by Raúl Jiménez-Tellado (ICREA-ICCUB) and Héctor Gil-Marín (ICCUB-IEEC).
 

RedH0T and the current cosmological model

Despite the remarkable success of the standard cosmological model over the last two decades, recent observations and distance measurements using a wide range of cosmological instruments suggest cracks in this scientifically accepted paradigm. Differences have appeared in the measurements of quantities (tensions) that the current cosmological model predicts to be equal. The most prominent tension concerns the Hubble parameter, which quantifies the expansion of the universe approximately 13 billion years after the Big Bang.

The goal of solving this cosmological challenge has been recognized with a Synergy Grant, a grant from the European Research Council that supports teams of two to four researchers to tackle research projects that require deep collaboration across different disciplines. In this call, 66 research groups have been recognized and will receive €684 million in funding.

Denario is a groundbreaking AI-powered tool poised to reshape the landscape of scientific research. Developed collaboratively by an international team of scientists from institutions such as the Flatiron Institute, Cambridge University, the Autonomous University of Barcelona, and the Institute of Cosmos Sciences of the University of Barcelona (ICCUB), Denario harnesses the capabilities of large language models to support researchers across every stage of the scientific process. From the initial spark of a hypothesis to the final interpretation of results, Denario offers a dynamic and modular system designed to enhance productivity and creativity in science.

At ICCUB, researchers Raúl Jiménez Tellado (ICREA-ICCUB), Pedro Tarancón (ICCUB), and Licia Verde (ICREA-ICCUB) played pivotal roles in both the technical development and conceptual framing of Denario. Jiménez and Tarancón demonstrated the tool’s potential by applying it to solve intricate problems in mathematical physics—an area where traditional AI systems often falter. Their work showcased Denario’s ability to engage with high-level theoretical challenges, pushing the boundaries of what AI can contribute to fundamental science.

Meanwhile, Licia Verde focused on the ethical dimensions of AI-assisted research. She helped shape the principles guiding Denario’s use, particularly in relation to transparency, accountability, and the evolving norms of scientific publishing. Her contributions have been instrumental in ensuring that Denario not only accelerates research but also aligns with responsible and rigorous scientific standards.

Denario itself is structured as a multi-agent system, with each AI agent specialized in a distinct task. These agents collaborate to assist with idea generation, literature review, data analysis, coding, debugging, and even manuscript writing. The system is built using AG2 and LangGraph frameworks, with cmbagent serving as the backend for research analysis. Users can interact with Denario through a command-line interface or a graphical user interface (DenarioApp), making it accessible to both technical and non-technical users.

One of Denario’s most innovative features is its ability to generate complete research papers, including figures and LaTeX-formatted manuscripts tailored to specific journal styles. For example, users can specify the APS (Physical Review) format and receive a ready-to-submit draft. The tool also allows manual input at any stage, enabling researchers to refine ideas, methods, or results with their own expertise.

Despite its capabilities, Denario is not intended to replace scientists. Its creators emphasize that it functions as an assistant, not an autonomous researcher. Human oversight remains essential, especially given that only a fraction of Denario’s outputs currently yield novel insights, and some results may include fabricated data. The tool’s value lies in its ability to streamline workflows, surface unexplored ideas, and foster interdisciplinary collaboration.

The ICCUB team’s involvement underscores the institute’s commitment to advancing both the technological and ethical frontiers of AI in science. Their work with Denario exemplifies how artificial intelligence can be integrated into research in a way that respects the integrity and creativity of scientific inquiry.

For further details, you can explore the Simons Foundation article or visit the Denario GitHub repository.

An international team led by ICREA researcher Mark Gieles from the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) and the Institute of Space Studies of Catalonia (IEEC) has developed a groundbreaking model that reveals how extremely massive stars (EMSs) – more than 1,000 times the mass of the Sun - shaped the birth and early evolution of the Universe’s oldest star clusters.

Published in Monthly Notices of the Royal Astronomical Society, the study shows how these short-lived stellar giants profoundly influenced the chemistry of globular clusters, some of the oldest and most enigmatic stellar systems in the cosmos.

Globular clusters: the ancient archives of the Universe

Globular clusters are dense, spherical groups of hundreds of thousands to millions of stars, found in nearly all galaxies including our Milky Way. Most of them are more than 10 billion years old, implying that they formed shortly after the Big Bang.

Their stars display puzzling chemical signatures - including unusual abundances of helium, nitrogen, oxygen, sodium, magnesium, and aluminum - that have defied explanation for decades. These “multiple populations” point to complex enrichment processes during cluster formation from extremely hot “polluters”.

A new model for cluster formation

The new study builds on the inertial-inflow model of massive star formation, extending it to the extreme environments of the early Universe. The researchers show that in the most massive clusters, turbulent gas naturally gives rise to extremely massive stars (EMSs) weighing between 1,000 and 10,000 solar masses. These accreting EMSs release powerful stellar winds rich in the products of hydrogen burning at high temperatures, which then mix with the surrounding pristine gas and forms the chemically distinct stars.

“Our model shows that just a few extremely massive stars can leave a lasting chemical fingerprint on an entire cluster,” says Mark Gieles. “It finally links the formation physics of globular clusters to the chemical signatures we observe today.”

Laura Ramirez Galeano and Corinne Charbonnel from the University of Geneva add: “It was already known that nuclear reactions in the centres of extremely massive stars could create the right abundance patterns. We now have a model that provides a natural path to form these stars in massive star clusters.”

This process unfolds rapidly - within 1 to 2 million years - before any supernovae explode, ensuring that the cluster’s gas remains free of supernova pollution.

A new window on the early Universe and black holes

The implications reach far beyond the Milky Way. The authors propose that the nitrogen-rich galaxies discovered by the James Webb Space Telescope (JWST) are likely dominated by EMS-rich globular clusters that formed during the earliest stages of galaxy assembly. “Extremely massive stars may have played a key role in shaping the first galaxies,” adds Paolo Padoan (Dartmouth College and ICCUB-IEEC). “Their luminosity and chemical yields naturally explains the nitrogen-enhanced proto-galaxies we’re now seeing in the early Universe with JWST.”

These colossal stars likely ended their lives collapsing into intermediate-mass black holes (more than 100 solar masses), which could possibly be found via gravitational-wave signals.

The research provides a unifying framework connecting star-formation physics, cluster evolution, and chemical enrichment. It suggests that EMSs were key engines of early galaxy formation, simultaneously enriching globular clusters and forming the first black holes.

Reference

Mark Gieles, Paolo Padoan, Corinne Charbonnel, Jorick S Vink, Laura Ramírez-Galeano, Globular cluster formation from inertial inflows: accreting extremely massive stars as the origin of abundance anomalies, Monthly Notices of the Royal Astronomical Society, Volume 544, Issue 1, November 2025, Pages 483–512, https://doi.org/10.1093/mnras/staf1314

For the first time ever, scientists have observed the nonlinear stage of modulational instability (MI) in a quantum system made of two repulsive components. This breakthrough, which features contributions from ICCUB researcher Alejandro Romero-Ros, was published in the prestigious journal Physical Review Letters.

The nonlinear stage of MI is a rare and complex wave phenomena caused by the exponential growth of perturbations which, until now, had only been seen in single-component systems with attractive interactions. In their experiment, the team created a Bose-Einstein condensate (BEC) (a state of matter where atoms behave like a single quantum entity) with two different hyperfine states of rubidium-87 atoms to show that, even in a purely repulsive environment, the nonlinear stage of MI can emerge and evolve into striking wave patterns.

Using a repulsive laser barrier to simulate a “dam-break” scenario, the researchers triggered the nonlinear stage of MI. This led to the formation of dispersive shock waves, which are localized high-oscillating ripples that appear when a wave breaks suddenly. In some cases, these waves collided and formed Peregrine solitons, rare and short-lived “rogue waves” that have applications across several disciplines.

The study also provides a general analytical framework for understanding how the nonlinear stage of MI expands in any two-component mixture, regardless of the ratio of particles, a tool that could be used in future research across many areas of physics.

“These results are relevant not just to quantum physics, but also to other nonlinear fields like fluid dynamics, optics, and plasma physics,” says Romero-Ros. “It’s a beautiful example of how atomic systems can serve as quantum simulators for much broader scientific questions.”

What makes this study especially powerful is its multidisciplinary approach: the experiments were conducted in a laboratory using ultracold atoms, mathematical models predicted how the waves would behave under different conditions and simulations, led by ICCUB researcher Alejandro Romero-Ros, helped bridge theory and experiment. His 1D simulations were crucial in identifying the right conditions to observe the nonlinear regime of MI, while 3D simulations confirmed the experimental results.

This work marks a major milestone in the study of nonlinear dynamics and quantum fluids and opens new avenues for exploring nonlinear wave behavior, with potential applications in quantum technologies, wave control, and even understanding natural phenomena like ocean rogue waves.

Reference:

Mossman, S., Mistakidis, S. I., Katsimiga, G. C., Romero-Ros, A., Biondini, G., Schmelcher, P., Engels, P., & Kevrekidis, P. G. Nonlinear Stage of Modulational Instability in Repulsive Two-Component Bose-Einstein Condensates. Physical Review Letters, 135(11), 113401 (2025). https://doi.org/10.1103/6jsr-f8q1