The most massive black holes in the Universe detected by the ripples they make in space time were not born directly from collapsing stars, according to a new study.

These cosmic giants instead build up through a series of repeated and extremely violent collision events in very densely populated star clusters, an international team of researchers argue.

Their study, led by Cardiff University, analysed version 4.0 of LIGO–Virgo–KAGRA’s Gravitational-Wave Transient Catalog (GWTC4), containing 153 sufficiently confident black hole merger detections.

The team wanted to test the idea that the heaviest black holes in GWTC-4 are second-generation objects, formed when earlier black holes merged and then merged again in the dense cores of star clusters, where stars can be packed up to a million times more tightly than in the Sun’s neighbourhood.

Their findings, published in Nature Astronomy, probe the origins of the heaviest black holes detected by their gravitational waves, revealing two distinct populations.

“Gravitational-wave astronomy is now doing more than counting black hole mergers,” explains lead author Fabio Antonini from Cardiff University’s School of Physics and Astronomy.  “It is starting to reveal how black holes grow, where they grow, and what that tells us about the lives and deaths of massive stars.”

“The ability to directly point to star clusters as the origin for these mergers, opens up the exciting possibility to use gravitational waves as completely new tool to learn about the formation and early evolution of dense star clusters that form in the early Universe,” says co-author Mark Gieles, ICREA research professor at the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) and the Institute of Space Studies of Catalonia (IEEC).

In the gravitational-wave data, the team identified:

• A lower-mass population consistent with ordinary stellar collapse
• A higher-mass population whose spins appear exactly like those expected if those black holes were formed by repeatedly merging with other black holes inside crowded groups of stars, rather than being born directly from single stars

“What surprised us most was how clearly the high-mass black holes stand out as a separate population,” recalls co-author Isobel Romero-Shaw, Ernest Rutherford Fellow at Cardiff University. 

“Unlike the lower-mass systems we analysed, which were generally slowly-spinning, the higher-mass systems are consistent with having more rapid spins, oriented in seemingly random directions. This is the exact signature you would expect if black holes were repeatedly merging in dense star clusters.

“That makes the cluster origin much more compelling than it was with earlier catalogues.”

The study also provides the strongest evidence yet for a “mass gap”, where extremely massive stars explode catastrophically rather than collapsing into black holes.

The long-predicted theory describes a forbidden mass range for black holes made directly from stars, where very massive stars are expected to be disrupted before they can form black holes.

The team pinpoints this range in a population of stellar-origin black holes 45 times the mass of the Sun and above.

Dr Antonini said: “In our study we find evidence for the long-predicted pair-instability mass gap — a range of masses where stars are not expected to leave behind black holes at all. Gravitational-wave detectors have successfully found black holes that appear to sit in or near that gap, which we identify at around 45 solar masses.

“So, the key question now is are these black holes telling us that our models of stellar evolution are wrong, or are they being made in another way?

“The biggest black holes in the current sample seem to be telling us about cluster dynamics, not just stellar evolution.

“Above about 45 solar masses the spin distribution changes in a way that is hard to explain with normal stellar binaries alone but is naturally explained if these black holes have already been through earlier mergers in dense clusters.”

The team also used this transition to shed light on an important nuclear reaction involved in helium burning inside massive stars.

“In the future, gravitational-wave data may help scientists study nuclear physics, because the mass limit set by pair instability depends on the nuclear reactions taking place in the cores of massive stars,” added co-author Fani Dosopoulou, a research associate at Cardiff University.

Reference

Antonini, F., et al. Gravitational waves reveal the pair-instability mass gap and constrain nuclear burning in massive stars. Nature Astronomy (2026). https://doi.org/10.1038/s41550-026-02847-0

The documentary "Gaia: de casa nostra a l'Univers", produced by Big Van Ciència with the support of a grant from the Catalan Foundation for Research and Innovation (FCRI), highlights Catalonia’s key role in one of the most ambitious scientific missions in recent history: the Gaia mission of the European Space Agency (ESA).

Thanks to Gaia, humanity has been able to map nearly two billion stars in the Milky Way with unprecedented precision. A fundamental part of this success has been developed in Catalonia, with teams from the University of Barcelona (UB), the Institute of Space Studies of Catalonia (IEEC), and the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) leading scientific contributions of top international level.

The premiere event will feature Teresa Sanchis, Director General for Research of the Government of Catalonia; Helena González, Director of Big Van Ciència; Xavier Luri, Full Professor in the Department of Quantum Physics and Astrophysics at the University of Barcelona, Director of the IEEC, and Principal Investigator of Gaia in Spain; Mercè Pallàs, Deputy for Coordination with UB Research Institutes; Maria Terrades, Director of the Barcelona Science Park; and Miquel Gómez, Director of the FCRI.

The event will combine institutional speeches, a screening of the documentary (35 minutes), and a science outreach show featuring humor and improvisation by Big Van Ciència, which will allow the audience to interact live with researchers from the Gaia mission.

The voice of Catalan science

“Gaia: de casa nostra a l'Univers” is not just a scientific documentary: it is a story about how research carried out in Catalonia is helping to transform global knowledge of our galaxy.

With more than 16,000 scientific publications derived from its data, Gaia has become a key tool for understanding the structure, origin, and evolution of the Milky Way. This documentary brings this scientific revolution closer to the general public, using an approachable and human tone, with touches of humor.

In the Gaia mission—the most ambitious project of the ESA to study the history and structure of the Milky Way—a team of astronomers and engineers from the Department of Quantum Physics and Astrophysics of the University of Barcelona, the ICCUB, and the IEEC has taken part since the very beginning, under the initial leadership of Professor Jordi Torra. Launched in 2013, the Gaia satellite has transformed our understanding of the cosmos through detailed stellar cartography of the positions, distances, motions, and properties of nearly two billion stars and other celestial objects.

Professor Xavier Luri highlights that “the UB Gaia team has worked on the mission since its beginnings, around 1997.” “Since then, it has taken part in all phases, from defining the scientific case and industrial design to data processing and scientific exploitation,” he continues. “Now, although Gaia has finished its observations, several years of work remain to fully process all the data collected during this period and to publish two additional data releases (DR4 and DR5),” the researcher concludes.

Black holes are often depicted as cosmic vacuum cleaners, but they are also powerful engines capable of launching jets: extremely fast streams of matter and energy shot out at nearly the speed of light. These jets strongly influence their surroundings, from nearby stars to entire galaxies. Yet one key question has remained unanswered: how powerful are these jets at any given moment?

A study published in Nature Astronomy has now achieved this long‑sought measurement by observing a jet that is quite literally bent sideways, and changing direction along the orbit.

The research focuses on the microquasar Cygnus X‑1, one of the most famous black holes in our Galaxy, located about 7,000 light‑years from Earth. The black hole orbits a massive, hot companion star that produces a powerful stellar wind — a constant stream of gas moving at thousands of kilometres per second.

Using almost 20 years of ultra‑sharp radio observations, the team discovered that this stellar wind pushes against the black hole’s jet, bending it as it travels through space. By modelling this interaction along the orbit, the researchers were able to directly calculate the jet’s power.

“The stellar wind acts like a natural probe,” explains Valentí Bosch‑Ramon, researcher at the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) and co‑author of the study. “By measuring how much the jet bends and changes direction with time, we can determine how strong it really is.”

Reading a jet from its bend

An everyday analogy helps: a strong stream of water from a hose remains straight on a calm day but bends if the wind blows hard enough. In Cygnus X‑1, the same principle applies on cosmic scales.

Using a technique called Very Long Baseline Interferometry (VLBI) (which combines radio telescopes across the Earth) astronomers obtained images sharp enough to detect tiny changes in the jet’s direction during the black hole’s orbit. The jet always bends away from the companion star, leaving no doubt that the stellar wind is responsible.

From this bending, the team measured a jet power of about 10³⁷ ergs per second.

This is an enormous amount of energy, comparable to the system’s total X‑ray output and, over the age of the system, similar to the energy released by a supernova explosion.

(An “erg” is a unit of energy used in astrophysics; 10³⁷ ergs per second is trillions of trillions of times more powerful than human technologies can produce.)

Although Cygnus X‑1 hosts a relatively small black hole (about 20 times the mass of the Sun), the same physics applies to supermassive black holes at the centres of galaxies. Their jets are thought to regulate how galaxies grow — a process known as black‑hole feedback.

“This measurement gives strong observational support to assumptions used in galaxy‑formation models,” says Bosch‑Ramon. “Understanding a nearby system like Cygnus X‑1 helps us better understand the role of black holes across the Universe.”

Beyond this specific system, the study introduces a new way to measure jet power directly, turning a complex interaction into a powerful scientific tool.

“What used to be considered a complication for modelling this system,” Bosch‑Ramon adds, “has become a unique opportunity to measure one of the most extreme phenomena in astrophysics.”

Reference
Prabu, S. et al. A jet bent by a stellar wind in the black hole X‑ray binary Cygnus X‑1. Nature Astronomy (2026).
https://doi.org/10.1038/s41550-026-02828-3

An international team led by researchers from the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) has developed a new method that could significantly improve our understanding of the expansion of the Universe and the nature of dark energy. The work has been published today in Nature Astronomy.

The study presents a powerful framework called CIGaRS that allows scientists to extract much more information from exploding stars known as Type Ia supernovae, using mainly images rather than expensive spectroscopic observations. The results pave the way for making the most of the enormous amount of data expected from the next generation of astronomical surveys, especially the Vera C. Rubin Observatory.

Why supernovae matter for understanding the Universe

Type Ia supernovae are the explosive deaths of white dwarf stars. Because they tend to explode with almost the same intrinsic brightness, astronomers use them as “standard candles”: by comparing how bright they really are with how bright they look from Earth, scientists can measure cosmic distances.

This technique played a key role in the discovery that the expansion of the Universe is accelerating, a phenomenon attributed to dark energy, one of the biggest mysteries in modern physics.

However, there is a catch: not all Type Ia supernovae are exactly the same.

The problem: supernovae are affected by their environments

Over the last two decades, astronomers have found that the brightness of these supernovae depends slightly on the galaxies in which they explode. For example, supernovae in more massive or older galaxies tend to look a bit different from those in smaller or younger ones.

Until now, these effects have usually been corrected using simple, approximate adjustments. This can limit how precisely we can measure the distances to these supernovae.

A unified solution: modelling everything together

The new study tackles this problem head-on by modelling everything at once: the supernova explosions, the galaxies hosting them, dust that dims and reddens their light, how often supernovae occur over cosmic time and even the expansion of the Universe itself.

Instead of analysing each piece separately, the researchers built a single, self-consistent model that links all these elements physically and statistically.

“A powerful way of modeling the Universe is to simulate it ab initio in the computer using bayesian inference,” explains Raúl Jiménez (ICREA-ICCUB), co-author of the study. “This provides a way to vary all possible parameters at the same time to predict what Universe we live in. Furthermore, by having this capacity one can look into possible “unknown unknown” systematics to understand their effect. The impact of these systematics in our inference is arguably the most important missing ingredient in current approaches to model the Universe.”

Artificial intelligence meets cosmology

To make this ambitious approach computationally feasible, the team used a modern set of techniques known as simulation-based inference.

In simple terms, the method works like this:

1. Scientists simulate many possible universes using physical models.
2. A neural network (a type of artificial intelligence) learns how simulated data relate to the underlying physical parameters.
3. The trained system can then infer those parameters directly from real observations.

This allows the analysis of tens of thousands of supernovae at once, something that would be impossible with traditional methods.

A key result: precise distances without spectroscopy

One of the most important outcomes is that the method can estimate galaxy distances (redshifts) very accurately using only images (Redshift is a measure of how much the light from a galaxy is stretched as the Universe expands. It tells us how far away, and how long ago, we are seeing it).

The new approach achieves a precision comparable to spectroscopic measurements, but without needing spectra. This is crucial because future sky surveys will discover millions of supernova candidates, while only a small fraction can realistically be studied with spectroscopy.

Preparing for the Rubin Observatory era

The Vera C. Rubin Observatory, currently under construction in Chile, will soon begin a ten-year survey of the sky, detecting an unprecedented number of supernovae. Around 99% of them will be observed only photometrically, meaning through images in different colours.

The CIGaRS framework is designed precisely for this scenario.

“Unlike other frameworks, which require analytic simplifications, our no-compromise end-to-end simulation-based inference approach is uniquely capable of extracting the full cosmological and astrophysical information from the Rubin Observatory's hard-earned data, while avoiding the pitfalls of selection and modelling biases.” says Konstantin Karchev (ICCUB-SISSA Trieste), lead author of the study. 

Beyond cosmology: learning how stars explode

In addition to improving measurements of dark energy, the study also sheds light on how and when Type Ia supernovae form. By reconstructing how supernova rates depend on the ages of stars in galaxies, the model helps address long-standing questions about their progenitor systems.

The results show that combining physics-based modelling with artificial intelligence can overcome key limitations in current cosmological analyses. According to the authors, this approach could improve cosmological constraints by up to a factor of four compared to traditional methods that rely only on a small, spectroscopically observed subset of supernovae.

With the Rubin Observatory set to transform astronomy in the coming years, methods like CIGaRS ensure that we will be ready to fully understand the data and the Universe it reveals.

Reference:

Karchev, K., Trotta, R. & Jiménez, R. CIGaRS I: Combined simulation-based inference from Type Ia supernovae and host photometry. Nature Astronomy (2026). https://doi.org/10.1038/s41550-026-02842-5

A new study led by researchers at the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) and the Institut d’Estudis Espacials de Catalunya (IEEC) reveals how the discs of galaxies like the Milky Way are impacted by ancient galactic collisions. 

Published in Monthly Notices of the Royal Astronomical Society, the research investigates how simulated galaxy collisions can fully or partially destroy stellar discs. Together with observational data of star clusters, the authors use this research to improve predictions for the time of the last significant galactic collision in our own Milky Way galaxy.
 

When did the Milky Way disc spin up?
 

The Milky Way disc is a vast, rotating system of stars shaped like a pancake, with spiral arms winding out from its centre. This disc contains most of the Galaxy’s stars, including the Sun, and rotates at a speed of over 220 kilometers per second.

Astronomers have long tried to determine when this rotating disc first formed. One key clue comes from the motions and ages of stars: at some point in the Galaxy’s early history, stars began to move in a coherent, rotating pattern, marking what scientists call the Galaxy’s “spin-up time.”

However, the Milky Way did not form in isolation. For decades, scientists suspected that a violent collision with a smaller galaxy played a major role in shaping the Milky Way we see today. This suspicion was confirmed in 2018, when data from the Gaia mission revealed a large population of stars whose unusual motions could only be explained by a massive merger around 10 billion years ago. This event is now known as the Gaia-Sausage-Enceladus (GSE) merger.

In this new study, simulations of Milky Way-like galaxies (the Auriga simulations) are used to investigate how rotating discs form under a variety of different scenarios. These show how galaxies like our Milky Way react to ancient collisions.
 

Key findings
 

The study shows that rotating stellar discs often form much earlier than previously assumed, but can be partially or completely destroyed by major galactic collisions. As a result, the moment when the Milky Way’s disc appears to “spin up” may not mark the first time a disc formed, but rather the time when the Galaxy recovered from a destructive merger.

Using insights from these simulations, the authors infer that the Gaia-Sausage-Enceladus merger likely occurred around 11 billion years ago, earlier than many previous estimates. Crucially, this timing coincides with a sharp increase in the birth of star clusters in the Milky Way. Such bursts of star formation are a natural consequence of galactic collisions, which compress gas and trigger intense star formation.

“Models of the Gaia-Sausage-Enceladus merger predict that a Galactic firework should have followed from the impact, raising star formation and fostering the formation of globular clusters. This is the first time this link has been made.” says collaborating author Chervin F. P. Laporte, researcher at CNRS.

“This research highlights the important relationship between galactic structure and ancient collisions, which must be understood in unison in order to understand the history of our Galaxy,” adds lead author Matthew D. A. Orkney, researcher at ICCUB and IEEC.

Whilst scientists can never travel back in time to observe the Milky Way in its youth, they can observe the formation of similar galaxies in the distant Universe with new data from the James Webb Space Telescope (JWST) and the Atacama Large Millimeter/submillimeter Array (ALMA), a powerful radio telescope.

Reference:

The full paper is available here, and the Auriga simulation data is publicly accessible for further research.

Orkney, Matthew; Laporte, Chervin. Build-up and survival of the disc: From numerical models of galaxy formation to the Milky Way. Monthly Notices of the Royal Astronomical Society. DOI: https://doi.org/10.1093/mnras/staf2154

The LISA mission has reached a key milestone in its development. The European Space Agency (ESA) has determined that the preliminary design of one of its subsystems—the Science Diagnostics Subsystem (SDS)—meets all mission requirements. This means ESA has given the green light to proceed to the detailed design phase, which will involve testing the system’s first prototypes.

Researchers from the Institute of Space Studies of Catalonia (IEEC) at the Institute of Space Sciences (ICE-CSIC) are leading the Spanish contribution to this project, providing their expertise to the development of the SDS instrument. The project also counts with the collaboration of the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) and the company Sener. 
 

ICCUB develops the radiation monitor for LISA 
 

The ICCUB team, led by Daniel Guberman, is developing the radiation monitor, a particle detector designed to measure the ionizing radiation flux affecting the LISA Test Masses—one of the mission’s most critical components. Owing to its unique design and location, the Radiation Monitor is also expected to contribute to fields such as Space Weather and Solar Physics.

The instrument has been conceived and built entirely at ICCUB. A central figure in its development, Roger Català, led the design and implementation of both the electronics and mechanical systems, playing a key role in shaping the instrument. Andreu Sanuy also contributed his expertise to the electronic design, while Albert Espiña was responsible for the software and firmware.

The simulations and experimental validation with prototypes were led by Marina Orta, with contributions from Pierpaolo Loizzo (INFN and visiting research fellow at ICCUB) and Roberta Pillera (INFN), supporting the development and validation of the system. One of the key components of the Radiation Monitor is the BETA ASIC, also developed at ICCUB by a team led by David Gascón. 

From concept to validation 

The LISA (Laser Interferometer Space Antenna) mission will consist of three spacecraft separated by 2.5 million kilometres that will form a gravitational wave detector, the first to operate from space. Each of the spacecraft will house a mass in freefall in its interior, which will allow, through laser measurements between them, the detection of the effect of low-frequency gravitational waves (0.1 mHz – 1 Hz). The mission will allow for the study of phenomena such as the merger of massive black holes or compact systems in our galaxy, and will expand our vision of the universe.

The SDS is one of the primary components of the mission's payload led by Spain. In total, the SDS subsystem will put more than one hundred sensors into orbit to measure temperature, magnetic fields, and radiation. These will monitor environmental fluctuations from both the satellite and the interplanetary environment with extreme precision. Detecting gravitational waves requires measuring incredibly weak forces—on the order of the weight of a single bacterium. Therefore, the SDS’s role in distinguishing the effects of gravitational waves from environmental noise is critical to the mission’s success.

The successfully passed evaluation, called PDR (Preliminary Design Review), is the culmination of a process that formally began at the start of the year. The most decisive moment took place on 25 February, when the team travelled to the European Space Research and Technology Centre (ESTEC), ESA's technical offices in Noordwijk (Netherlands), to review and resolve the open points regarding this key mission system.

The LISA mission, led by ESA, receives funding from the Ministry of Science, Innovation and Universities of Spain through the Spanish Space Agency (AEE). 

Nadejda Blagorodnova Mujortova, a researcher at the Institute of Cosmos Sciences of the University of Barcelona, ​​the Institute of Space Studies of Catalonia (ICCUB-IEEC) and professor at the Faculty of Physics, has jointly received the 2025 National Research Award for Young Talent, with Katherine Villa Gómez, ICREA research professor and group leader at the Institute of Chemical Research of Catalonia (ICIQ). The announcement was made today by the Catalan Minister for Research and Universities, Núria Montserrat, at a press conference.

The award carries a €15,000 endowment, which is equally shared between the two awardees.

Nadejda Blagorodnova Mujortova's

research focuses on observational astronomy in the time domain, which studies transient astrophysical phenomena such as supernovae, stellar mergers, and stars disrupted by supermassive black holes.

With the research group Common Envelope Transients - Progenitors, Precursors, and Properties of their Outbursts (CET-3PO), funded by a grant from the European Research Council (ERC), she studies the interaction and merger of close binary stars. These studies combine stellar evolution models with observations from the most advanced ground-based telescopes, such as the Gran Telescopio Canarias, the Very Large Telescope (Chile), and the Southern African Large Telescope (South Africa), as well as observations Hubble Space Telescope and James Webb Space Telescope.

“I sincerely thank the Catalan Foundation for Research and Innovation for this recognition, which gives visibility to new generations of researchers. This award represents an incentive to continue working with passion and to reinforce research excellence and innovation,” says Blagorodnova.

Other awardees

The other categories of the National Research Awards were also announced today. Luis Serrano, director of the Centre for Genomic Regulation (CRG), has been awarded the 2025 National Research Award for his pioneering research in systems biology and protein design.

The National Research Award for Knowledge Transfer and Innovation went to the Eurecat Foundation, and the Joan Guinovart and Cirera Award for Science

Communication was given to biochemist and science communicator Pere Estupinyà. The National Award for Patronage and Public-private Scientific Collaboration has been given to the ARI Project, of Hospital Clínic and the August Pi i Sunyer Biomedical Research Institute (IDIBAPS), and the National Award for the Creation of a Science-based Company, was given to the University of Lleida and the University of Sherbrooke (Canada), for their start-up UniSCool.

That the universe is expanding has been known for almost a hundred years now, but how fast? The exact rate of that expansion remains hotly debated, even challenging the standard model of cosmology. A research team led by the Technical University of Munich (TUM), and with the participation of ICREA-ICCUB-IEEC researcher Frédéric Courbin, has now imaged and modelled an exceptionally rare supernova that could provide a new, independent way to measure how fast the universe is expanding.

The supernova is a rare superluminous stellar explosion, 10 billion lightyears away, and far brighter than typical supernovae. It is also special in another way: the single supernova appears five times in the night sky, like cosmic fireworks, due to a phenomenon known as gravitational lensing.

Two foreground galaxies bend the supernova’s light as it travels toward Earth, forcing it to take different paths. Because these paths have slightly different lengths, the light arrives at different times. By measuring the time delays between the multiple copies of the supernova, researchers can determine the universe’s present-day expansion rate, known as the Hubble constant.

Sherry Suyu, Associate Professor of Observational Cosmology at TUM and Fellow at the Max Planck Institute for Astrophysics, explains: “We nicknamed this supernova SN Winny, inspired by its official designation SN 2025wny. It is an extremely rare event that could play a key role in improving our understanding of the cosmos. The chance of finding a superluminous supernova perfectly aligned with a suitable gravitational lens is lower than one in a million. We spent six years searching for such an event by compiling a list of promising gravitational lenses, and in August 2025, SN Winny matched exactly with one of them.”

High-resolution color image of unique supernova

Because gravitationally lensed supernovae are so rare, only a handful of such measurements have been attempted to date. Their accuracy depends strongly on how well one can determine the masses of the galaxies acting as a lens, because these masses control how strongly the supernova’s light is bent. To measure those masses, the team obtained images with the Large Binocular Telescope in Arizona, USA, using its two 8.4-meter diameter mirrors and an adaptive optics system that corrects for atmospheric blurring. The result is the first high-resolution color image of this system published to date.

The observations reveal the two foreground lens galaxies in the center and five bluish copies of the supernova — reminiscent of a firework exploding. This is quite unusual, since galaxy-scale lens systems normally produce only two or four copies. Using the positions of all five copies, Allan Schweinfurth and Leon Ecker, junior researchers in the team, built the first model of the lens mass distribution.

“Until now, most lensed supernovae were magnified by massive galaxy clusters, whose mass distributions are complex and hard to model,” says Allan Schweinfurth. “SN Winny, however, is lensed by just two individual galaxies. We find overall smooth and regular light and mass distributions for these galaxies, suggesting that they have not yet collided in the past despite their close apparent proximity. The overall simplicity of the system offers an exciting opportunity to measure the universe’s expansion rate with high accuracy.”

ICCUB expertise in time-delay measurements

Frédéric Courbin has long been a leading figure in the field of time-delay cosmography. Courbin pioneered the field of time delay measurements in lensed quasars with the COSMOGRAIL program, which has provided some of the most precise measurements of the Hubble constant using gravitational lensing techniques.

His experience in long-term monitoring of gravitational lenses was instrumental in the present work. In particular, he organized the observations at the Maidanak Observatory, whose data have already been crucial in the past for monitoring lensed quasars and are now contributing to the study of this exceptional lensed supernova.

“It is particularly impressive to finally see a supernova lensed by a galaxy and with measurable delays. This will be done in the near future, in particular with Maidanak observations, which have already been crucial in the past for the observations of lensed quasars,” says Frédéric Courbin.

Two methods, two very different results

So far, scientists have mostly relied on two methods to measure the Hubble constant, but these methods yield conflicting results. This puzzle is known as the Hubble tension.

The first is the local method, which measures distances to galaxies one step at a time, much like climbing a ladder, where each step depends on the previous one; hence, it is referred to as the cosmic distance ladder. It uses objects with well-known brightness to estimate distances and then compares those distances with how fast galaxies are moving away. Because this method involves many calibration steps, even small errors can accumulate and affect the final result.

The second method looks much farther back in time. It studies the cosmic microwave background, the faint afterglow of the Big Bang, and uses models of the early universe to calculate today’s expansion rate. This approach is highly precise, but it relies heavily on assumptions about how the universe evolved, and these assumptions are still subject to debate.

A new, one-step approach

A third, independent method now enters the picture: using a gravitationally lensed supernova. Stefan Taubenberger, a leading member of Professor Suyu’s team and first author of the supernova-identification study, explains that by measuring the time delays between the multiple copies of the supernova and knowing the mass distribution of the lensing galaxy, scientists can directly calculate the Hubble constant: “Unlike the cosmic distance ladder, this is a one-step method, with fewer and completely different sources of systematic uncertainties.”

Astronomers worldwide are currently observing SN Winny in detail using both ground-based and space-based telescopes. Their results will provide crucial new insights and help clarify the long-standing Hubble tension.

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