A group of scientists led by the Leibniz Institute for Astrophysics Potsdam (AIP) and the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) have used novel machine learning tecniques to process data for 217 million stars observed by the Gaia mission in an extremely efficient way, which opens up exciting opportunities to map characteristics like interstellar extinction and metallicity across the Milky Way, aiding in the understanding of stellar populations and the structure of our galaxy. They published their results in Astronomy and Astrophysics.

With the third data release of the European Space Agency’s Gaia space mission, astronomers gained access to improved measurements for 1.8 billion stars, which provides a vast amount of data for researching the Milky Way. However, analysing such a large dataset efficiently presents challenges. In the now published study, researchers explored the use of machine learning to estimate key stellar properties using Gaia's spectrophotometric data. The model was trained on high-quality data from 8 million stars and achieved reliable predictions with small uncertainties. 
“The underlying technique, called extreme gradient-boosted trees allows to estimate precise stellar properties, such as temperature, chemical composition, and interstellar dust obscuration, with unprecedented efficiency. The developed machine learning model, SHBoost, completes its tasks, including model training and prediction, within four hours on a single GPU - a process that previously required two weeks and 3000 high-performance processors,” says Arman Khalatyan from AIP and first author of the study. “The machine-learning method is thus significantly reducing computational time, energy consumption, and CO2 emission.” This is the first time such a technique was successfully applied to stars of all types at once.
The model trains on high-quality spectroscopic data from smaller stellar surveys and then applies this learning to Gaia’s large third data release (DR3), extracting key stellar parameters using only photometric and astrometric data, as well as the Gaia low-resolution XP spectra. “The high quality of the results reduces the need for additional resource-intensive spectroscopic observations when looking for good candidates to be picked-up for further studies, such as rare metal-poor or super-metal rich stars, crucial for understanding the earliest phases of the Milky Way formation”, says Cristina Chiappini from AIP. This technique turns out to be crucial for the preparation of future observations with multi-object spectroscopy, such as 4MIDABLE-LR, a large survey of the Galactic Disc and Bulge that will be part of the 4MOST project at the European Southern Observatory (ESO) in Chile.
“The new model approach provides extensive maps of the Milky Way’s overall chemical composition, corroborating the distribution of young and old stars. The data shows the concentration of metal-rich stars in the Galaxy’s inner regions, including the bar and bulge, with an enormous statistical power.“ adds Friedrich Anders from ICCUB.
The team also used the model to map young, massive hot stars throughout the Galaxy, highlighting distant poorly studied regions in which stars are forming. The data also reveal that there exist a number of “stellar voids” in our Milky Way, i.e. areas that host very few young stars. Furthermore, the data demonstrate where the three-dimensional distribution of interstellar dust is still poorly resolved. 

As Gaia continues to collect data, the ability of machine-learning models to handle the vast datasets quickly and sustainably makes them an essential tool for future astronomical research. The success of the approach demonstrates the potential for machine learning to revolutionise big data analysis in astronomy and other scientific fields while promoting more sustainable research practices.

Reference: https://www.aanda.org/component/article?access=doi&doi=10.1051/0004-6361/202451427

A study published in the journal Nature has discovered 55 high-speed stars ejected from the young star cluster R136, located in the Large Magellanic Cloud — a satellite galaxy of the Milky Way — some 160,000 light-years away. This finding increases the number of known runaway stars in this region of the cosmos tenfold and is a new scientific contribution from the European Space Agency’s (ESA) Gaia telescope, which aims to identify the positions, distances and speed of more than a billion stars in our galaxy.

This is the first time that such a large number of high-speed stars have been detected coming from a single cluster. In particular, R136 is a cluster of particular characteristics, containing hundreds of thousands of stars, including the most massive stars known (up to three hundred times the mass of the Sun), and is part of the largest known star-forming region within five million light-years.

Runaway stars launched from the young cluster R136 — beyond the moon, at a distance of 1.5 million kilometres from Earth — have been identified at extremely far distances for the Gaia mission, ESA’s most ambitious project to detail the stellar mapping of our galaxy. Since its inception, astronomers from teams at the Department of Quantum Physics and Astrophysics of the University of Barcelona, the Institute of Cosmos Sciences of the UB (ICCUB) and the Institute of Space Studies of Catalonia (IEEC) have been participating in the Gaia project.

The new study, led by experts from the University of Amsterdam, Leiden University and Radboud University (the Netherlands), is co-authored by Dr. Mark Gieles, (ICREA, ICCUB, IEEC). Astronomers from the Royal Observatory of Belgium (Belgium), Tel Aviv University (Israel), the Netherlands National Institute for Space Research (The Netherlands) and the University of Geneva (Switzerland) have also signed the paper.

Runaway stars at high speeds in the Large Magellanic Cloud

When star clusters form, collisions between smaller star clusters can cause the ejection of stars from the young cluster. The science team led by Mitchel Stoop, a PhD student at the University of Amsterdam, has found that the young cluster R136 has ejected up to a third of its most massive stars outwards in the last few million years, at speeds of over 100, 000 km/h. These stars travel up to 1,000 light-years from their birthplace before exploding as supernovae at the end of their stellar life and giving rise to a neutron star or black hole.

Another surprising result of the study indicates that there was not a single period when stars were dynamically ejected, but two. According to Scoop, “the first episode was 1.8 million years ago, when the cluster formed, and fits with the ejection of stars during the formation of the cluster”. “The second episode was only 200,000 years ago and had very different characteristics. For example, the runaway stars of this second period moved more slowly and did not shoot off in random directions as in the first episode, but in a preferred one”, says the expert.

Gieles, from ICREA, ICCUB and IEEC and co-author of the research, says that “a lot happens in a short time during the formation of massive star clusters and the images only provide a snapshot”. He adds that “these new observations of the motion of escaping stars are like a ‘rearview mirror’, giving us an unprecedented view of what happened before”.

It is worth recalling that the Dutch astronomer Adriaan Blaauw (1914-2010) identified the first indications of the existence of runaway stars, i.e. stars moving at high speed through the Milky Way. With this discovery, Blaauw opened one of the most exciting and surprising chapters in astronomy and cosmology research, which has been unravelling its mysteries thanks to an initial ESA mission — called Hipparcos — and now with the Gaia telescope.

Reference article:

Stoop, Mitchell; de Koter, Alex. et al. «Two waves of massive stars running away from the young cluster R136». Nature, October 2024. DOI: 10.1038/s41586-024-08013-8
 

Licia Verde, ICREA researcher and Scientific Director of the Institute of Cosmos Sciences of the University of Barcelona, has been awarded the 2024 Medal by the Real Sociedad Española de Física (RSEF) and the BBVA Foundation. This prestigious prize celebrates Prof. Verde's significant contributions to cosmology, particularly in the study of the universe's expansion history, dark matter, and dark energy. Her research has been instrumental in shaping our understanding of the standard cosmological model. 

The RSEF-Fundación BBVA awards, presented annually, are among the most prestigious recognitions in Spain for contributions to physics. These awards honour groundbreaking work in various fields of physics, as well as outstanding educational and outreach efforts. The Medal is awarded to a physicist whose work has had an enduring and far-reaching impact on the field. Verde’s pioneering research has contributed significantly to our understanding of the fundamental properties of the cosmos, earning her global recognition. 

“My most sincere thanks to the committee,” says Prof. Verde, “And also, to my mentors and to everyone who has supported me and to all the researchers in training who passed through my group; In research, “it takes a whole village””. 

The ICCUB warmly congratulates Licia Verde for this remarkable achievement, which will be added to her extensive list of recognitions and marks the excellence of the research carried out at our institution. 

For more information on the RSEF-Fundación BBVA awards, visit the Fundación BBVA website. 

Mar Carretero-Castrillo, a predoctoral researcher of the Institute of Cosmos Sciences of the University of Barcelona and the Institute of Space Studies of Catalonia (ICCUB-IEEC), has been named a finalist for the 2024 La Vanguardia Science Award. This recognition follows her role as the first author of the groundbreaking discovery of numerous massive runaway stars in the Milky Way, alongside Drs. Marc Ribó and Josep M. Paredes, a finding that offers new insight into the stellar evolution of massive stars.

The discovery, made possible through data from the European Space Agency’s Gaia mission, identified a population of massive runaway stars that have been ejected from their birthplaces due to changes in gravitational forces, travelling at high velocities within the galaxy. These findings provide vital clues to understanding the critical processes in massive stellar evolution that lead to their ejection from stellar clusters or from binary systems after supernova explosions.

Mar Carretero-Castrillo, who leads the study, emphasised the importance of these discoveries: “the identification of so many massive runaway stars opens the door to discover new interesting astrophysical sources. We have released the catalogues of the runaway stars found in open format to the scientific community to maximise the exploitation of the potential discoveries”. 

This groundbreaking research not only expands our understanding of massive star dynamics but also sets the stage for further investigations into high-energy systems associated with runaway stars. 

In recognition of her pioneering research, Mar Carretero-Castrillo has been selected as a finalist for the La Vanguardia Science Award, which aims to honour women leading scientific contributions across Spain and help reduce the gender gap in science. The award celebrates research that drives innovation and enhances global understanding.

La Vanguardia and the Fundació Catalunya La Pedrera, which have jointly organized the award since 2011, invite readers to choose the winning research in a vote that will be open until Sunday, October 20.

The prize will be awarded to the three researchers that receive the most votes and will be presented at an event open to the public, which will be held on November 27, in La Pedrera.

For more information about Mar Carretero-Castrillo’s study, please visit the following website or the original article “Galactic runaway O and Be stars found using Gaia DR3⋆” .

Adriana Nadal, a predoctoral researcher at the Physical Cosmology group at the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) and the Institute of Space Sciences of Catalonia (IEEC), has been awarded the Jordi Porta i Jué Award by the Catalan Society of Physics of the Institute of Catalan Studies (IEC). Nadal was honored for her master’s thesis titled "Testing the robustness of the BAO determination in the presence of massive neutrinos," completed as part of the Master's in Astrophysics, Particle Physics and Cosmology at the University of Barcelona.

The award ceremony took place on Tuesday, April 23rd, coinciding with Sant Jordi's Day, at the IEC social quarters and was presided over by IEC President Teresa Cabré. The Jordi Porta i Jué Award is a significant component of the IEC’s Sant Jordi Awards, which aim to promote scientific research and the dissemination of all elements of Catalan culture.

Nadal’s master thesis made significant contributions to the field of cosmology, focusing on the Baryon Acoustic Oscillation (BAO), one of the primary probes of cosmology today. Her research studied and quantified the impact of built-in assumptions of the data analysis pipeline on the measurement of the isotropic BAO peak, particularly in the context of massive neutrinos. This work was supervised by ICCUB researchers Héctor Gil Marin (ICCUB-IEEC) and Licia Verde (ICREA-ICCUB).

Now continuing her academic journey, Adriana Nadal is a predoctoral researcher at ICCUB, where she is working on her doctoral thesis titled "Developing tools for the analysis of DESI data employing higher-order statistics," under the guidance of Héctor Gil Marin and Licia Verde. Her ongoing research promises to further advance our understanding of the universe through innovative analytical techniques.

For more information about Adriana Nadal's research and the work of the Physical Cosmology group at ICCUB, please visit ICCUB’s website.

More than two hundred international experts will take part in the 10th International Conference on Quarks and Nuclear Physics (QNP2024), a scientific summit organized by the UB Institute of Cosmos Sciences (ICCUB), which will be held in the Aula Magna of the Faculty of Biology at the University of Barcelona from 8 to 12 July. This meeting, hosted by the UB for the first time, will bring together world experts in the fields of nuclear physics and hadronic physics to discuss the latest advances in theory, experimentation and technology and to address the scientific challenges of the 21st century regarding the nature and phenomena related to the essential components of matter in the universe.

In previous editions, this date with the world of nuclear physics was held in the cities of Adelaide (Australia), Jülich (Germany), Bloomington (United States), Madrid (Spain), Beijing (China), Palaiseau (France), Valparaíso (Chile), Tsukuba (Japan) and Tallahassee (United States).

The meeting will be inaugurated by the rector, Joan Guàrdia, on Monday, 8 July, in an event in which will participate the professors Xavier Luri and Àngels Ramos, from the Faculty of Physics and the ICC, and M. José García Borge, from the Institute of the Structure of Matter (IEM, CSIC). This will be followed by lectures by Juan M. Nieves, from the University of Valencia, entitled “Charge-conjugation asymmetry and molecular content: the Tcc(3875) and Ds(2317) in nuclear matter”, and Takashi Nakatsukasa, from the University of Tsukuba (Japan), with the paper “Energy density functional approaches to inhomogeneous superfluid neutron-star matter”.

Discovering yet unknown phenomena in nuclear physics

One of the most shocking discoveries in the world of physics was the Higgs boson, announced in July 2012 and postulated theoretically in 1964 by the scientist Peter Higgs to explain the essential building blocks of matter. The discovery is a major milestone at CERN’s Large Hadron Collider (LHC) in Geneva (Switzerland), one of the main scientific infrastructures that are shedding new light on the world of particle physics to understand its nature and the interaction mechanisms that are still unknown to the research community.

“Nuclear and hadronic physics in the 21st century present a number of fascinating scientific challenges, such as the fundamental understanding of strong interactions, the study of new exotic hadrons, the development of more precise nuclear models and the exploration of new states of matter”, says Xavier Luri, professor at the Department of Quantum Physics and Astrophysics and director of the ICCUB.
“It is worth noting that advances in nuclear and hadronic physics have a major impact on other areas of knowledge. In the field of astrophysics, for example, research to create new elements will help to understand the phenomenon of nucleosynthesis in the universe, and studies to characterize the behaviour of nuclear matter under extreme conditions will help to understand the properties and internal composition of neutron stars. In the field of particle physics, experiments on the double beta decay of nuclei, which seek to elucidate the nature of neutrons, will explore the limits of the standard model, while very precise measurements of nuclear and hadronic processes could lead to the detection of dark matter”, adds Luri.

Beyond the standard model of particle physics

The new edition of the international conference will address the limits of knowledge beyond the standard model that describes the most fundamental forces and particles in the universe. Theorists and experimentalists will discuss the progress of recent advances in hadronic and nuclear physics, and share the most revealing results on the structure of quarks and gluons in hadrons, decays and interactions between different particles, cold dark matter and large scientific-technical equipment, among others.

“Very precise measurements of the properties of nuclei and hadronic interactions are needed to discover ‘new physics’ phenomena, i.e. those that cannot be explained by the standard model of particle physics. Sophisticated theoretical studies of certain hadronic processes now show that the degree of precision needed to detect possible candidates for the elusive dark matter (which makes up 85% of the mass of our universe!) is beginning to be achievable in large experimental facilities, such as the Large Hadron Collider (LHC) at CERN”, says Professor Àngels Ramos, head of the UB’s Theoretical Nuclear Physics and Many Interacting Particles Group and coordinator of the conference.

“Another possible manifestation of ‘new physics’ could come from underground laboratories, such as the Canfranc laboratory (LSC), where the so-called double beta decay of nuclei without neutrino emission is being searched for, which will help to elucidate the nature of neutrinos and their mass hierarchy”, says Ramos.

To discuss new research horizons, the conference will feature internationally renowned experts such as Tomohiro Uesaka, head of the Nuclear Dynamics Research Group at the RIKEN centre in Japan, author of significant experimental contributions to the properties of exotic nuclei — rich in neutrons — that test modern theories of nuclear structure; Laura Fabbietti, from the Technical University of Munich (Germany) and the LHC ALICE collaboration, who has led the use of femtoscopy to characterize interactions between unstable hadrons; Yvonne Leifels, head of the Research Division of the Helmholtz Centre for Heavy Ion Research (GSI), who will present the scientific prospects of FAIR (Germany), the ion collider that will allow us to understand how elements are synthesized in the universe or the composition of matter under extreme conditions of density and temperature, and Eulogio Oset, theoretical physicist at the University of Valencia, internationally recognized for his outstanding contributions in the fields of hadronic physics and nuclear physics, and distinguished with the medal of the Royal Spanish Physics Society 2023.

Within the framework of the conference, and in collaboration with the Fundaciño Catalunya La Pedrera, Professor Freya Blekman, from the German Electron Synchrotron (DESY, University of Hamburg), will give the talk “Understanding the Large Hadron Collider: What, why and how?”, on Wednesday 10 July, at 6.30 p.m., in the auditorium of the Casa Milà (La Pedrera). The talk, open to the public, will focus on the research activity at the LHC in Geneva — the Swiss Army Knife of experiments, which investigates everything from new particles and forces to the birth of the universe — without neglecting the more fun and social aspects of this exceptional scientific facility.

The 10th International Conference on Quarks and Nuclear Physics is supported by the Barcelona City Council, the Fundació Catalunya La Pedrera, the International Union of Pure and Applied Physics (IUPAP) and the European Committee for Nuclear Physics Collaboration (NuPECC), which is one of the expert committees of the European Science Foundation (ISF).

The ILIADA project, led by scientists from the Institute of Space Sciences (ICE-CSIC) and the Institut d'Estudis Espacials de Catalunya (IEEC) and in collaboration with the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) and the Universitat Politècnica de Catalunya - BarcelonaTech (UPC), has been selected to test technology on board the next microsatellite of the NewSpace Strategy.

Last February, the Government of Catalonia and the Institute of Space Studies of Catalonia (IEEC — Institut d’Estudis Espacials de Catalunya) opened the call for the selection of the payload as an in-orbit technology demonstrator (IOD) to be embarked on the new Earth Observation satellite mission. This mission will give continuity to the Menut mission in the framework of the NewSpace Strategy of Catalonia, promoted by the Government of Catalonia with the collaboration of the IEEC, the i2CAT Foundation and the Cartographic and Geological Institute of Catalonia (ICGC).

The call aimed to offer the opportunity to companies, organisations or research centres based in Catalonia to present one of its innovative technologies to integrate it into the platform of this new satellite, with the aim of validating it in orbit, accelerate its introduction into the market or demonstrate additional capabilities.

The call aimed to offer the opportunity to companies, organisations or research centres based in Catalonia to present one of its innovative technologies to integrate it into the platform of this new satellite, with the aim of validating it in orbit, accelerate its introduction into the market or demonstrate additional capabilities.

After analysing all the applications received, the evaluation committee appointed by the Government of Catalonia and the IEEC has decided that the proposal IN-ORBIT LISA DIAGNOSTICS DEMONSTRATOR (ILIADA) will have the opportunity to integrate and fly on board the next microsatellite that will provide the fourth mission of the NewSpace Strategy of Catalonia to try to achieve the technical and scientific objectives it has proposed.

The ILIADA project will implement a first version of the Scientific Diagnostics Subsystem (SDS) sensors, the Spanish contribution to the LISA (Laser Interferometer Space Antenna) mission of the European Space Agency (ESA), which will put a gravitational wave observatory in space for the first time, as well as innovative sensor concepts developed in the IEEC framework. Through the use of high-precision magnetometers and the on-board radiation monitor, ILIADA will attempt to detect the electric currents that align with the Earth’s magnetic field lines as they pass through the poles. These measurements are used to better understand how our magnetic field is generated and can provide new insights into space weather, i.e. the real-time measurement and analysis of the set of physical properties of the Sun, the interplanetary medium, the magnetosphere, the atmosphere and the Earth’s surface that are influenced, directly or indirectly, by solar activity. Understanding space weather is important because of the impact it can have on our infrastructures, technology, society and health.

The ILIADA project is led by researchers and members of the IEEC at the Institute of Space Sciences (ICE-CSIC), with the collaboration of the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) and the Universitat Politècnica de Catalunya – BarcelonaTech (UPC). Specifically, the groups involved are the following: Gravitational Astronomy – LISA (CSIC), Micro and Nano Technologies (UPC), the Technological Unit – instrumentation division (UB), and the Centre for Space Studies and Research – CERES, together with the engineering group 3Cat-Gea (IEEC).

The ICCUB Technology Unit is developing the radiation monitor for the LISA mission. The team, led by Daniel Guberman (ICCUB-IEEC), is preparing a reduced version for the ILIADA mission, that will be sent to be tested on a SmallSat together with the other LISA diagnostic systems developed by the IEEC.

Thanks to the Gaia mission, the European Space Agency’s (ESA) most ambitious project to detail the stellar mapping of our galaxy, a massive stellar black hole, Gaia BH3, has been discovered in the Milky Way. This type of black hole has been found before in distant galaxies by gravitational-wave observations, and is now identified for the first time in our galaxy. It is a dormant black hole, is the second closest to Earth — at a distance of 590 pc (or 1926 light-years) — is about thirty-three solar masses and forms a large binary system with its companion star.
This exceptional discovery confirms some theories and needs revision as well. This is an exciting result for the astronomical community, which raises the question of how many such black holes there are in space, or what mass ranges of black holes the Gaia mission will be able to discover.

This finding, published in the prestigious journal Astronomy & Astrophysics, involved a team of astronomers and engineers from the Department of Quantum Physics and Astrophysics, the Institute of Cosmos Sciences (ICCUB) of the University of Barcelona and the Institute of Space Studies of Catalonia (IEEC), who have been part of the Gaia mission, the most ambitious project of the European Space Agency (ESA) to study the history and structure of the Milky Way.

How can a dormant black hole be detected?

If the black hole is dormant, doesn’t that make it hard to spot it? Most known black holes are detected through the X-rays they emit when material from their stellar companion is “eaten”. With dormant black holes, little or no radiation is emitted by the source, so the black hole can only really be seen because of the gravitational effect it exerts on its companion star. Dormant black holes had never been detected before the Gaia mission. In particular, after the release of the third Gaia data release — the Gaia Data Release (DR3) — the first dormant black holes in our galaxy could be identified: Gaia BH1 and Gaia BH2.
"It's a real unicorn! It's like nothing we have ever seen," says expert Pasquale Panuzzo, from the Paris Observatory of the Centre National de la Recherche Scientifique (CNRS) in France, and lead author of the paper. “This is the kind of discovery you make once in your research life. So far, black holes this big have only ever been detected in distant galaxies by the LIGO–Virgo–KAGRA collaboration, thanks to observations of gravitational waves.”

In the validation of the preliminary data processed by Gaia Data Release (DR4), and given the preliminary results for the non-single star pipeline, this galactic source required further checks to see if the detected data were correct or corrupt. At first, the Data Processing and Analysis Consortium (DPAC) team considered that these results could not be real. After many internal verifications, all the data suggested that it was a genuine detection, a scientific finding that is worth publishing before the release of the Gaia Data Release (DR4) to allow further follow-up of the discovery by the scientific community.

“While in the previous data release (Gaia DR3) we identified quite a few spurious black hole candidates that were traced back to data calibration issues, the quality of the latest data reduction has improved so much that we expect to publish quite a number of genuine black holes in Gaia DR4!” says Berry Holl of the Geneva Observatory, a member of the Gaia Collaboration.
“It’s impressive to see the transformational impact Gaia is having on astronomy and astrophysics,” notes Carole Mundell, ESA Director of Science. “Its discoveries are reaching far beyond the original purpose of the mission, which is to create an extraordinarily precise multidimensional map of more than a billion stars throughout our Milky Way."

The most massive black hole of stellar origin in our Galaxy

But what makes this finding so amazing? Most of all because of its high mass. With thirty-three solar masses, Gaia BH3 is not only the most massive black hole of stellar origin known in our galaxy, but it is also in line with results obtained by gravitational-wave observatories such as LIGO/VIRGO/KAGRA. These facilities found a population of black holes with masses that contradict models of stellar evolution through the observation of gravitational waves from black hole mergers. The Gaia finding confirms that massive black holes of stellar origin also exist in our own Milky Way.

Most black holes of stellar origin in our galaxy have a mass of about ten solar masses, and its record value until now was held by the Cyg X-1 black hole, with an estimated mass of about twenty times that of the Sun. Gaia BH3 goes much further and is the record for our galaxy. Its mass is pinned down with unparalleled accuracy as well (32.7 +/- 0.82 M_solar), putting it firmly in the 30 solar mass range.
“The mass distribution for the black hole population derived from gravitational wave observations shows a clear peak around thirty solar masses”, says Tsevi Mazeh of Tel Aviv University, a member of the Gaia Collaboration. “It is very interesting to see now that Gaia BH3 is right at this peak with its 33 solar masses. This provides strong scientific support for the existence of this peak”, he adds.

The second closest black hole to Earth

This black hole, which lies at a distance of 1926 light-years, is currently the second closest to Earth. Why is this black hole only visible now? The longer time span of observations that will form the basis of Gaia Data Release 4 (DR4) is crucial for answering this question. The orbit of the stellar companion around their common centre of mass is estimated to be 11.6 years. This means that, with 5.5 years of data being processed for the next DR4, Gaia can map half of its orbit. This is enough to distinguish the additional oscillation in the position and motion of the companion star. It is expected that, with a longer time period of Gaia observations, more and more wide binaries can be identified. Lots of results are therefore to be expected from Gaia’s data releases.

“In the visible wavelength range and the infrared, the light from the visible companion star outshines anything that might come from Gaia BH3 itself — or else the black hole would have been discovered much earlier, and without Gaia” says Uli Bastian, member of the Gaia Collaboration.

Comparison of the orbits of Gaia's black holes and their companion stars. To give insight in the orbit, the orbits of the Gaia BH3 system are projected onto the Solar System, with the Sun in the zero point. Gaia's black holes are dormant black holes detected due to the wobble seen in the position and motion of its companion star. It can be clearly seen that the star orbiting Gaia BH3 is in a wide orbit around their mutual centre of mass. These wider orbits are more easily distinguishable with longer time spans of observations. The orbital period of 11.6 years is about twice the time span of observations that will form the basis for Gaia Data Release 4.Also available as dark version here. Credits: ESA/Gaia/DPAC - CC BY-SA 3.0 IGO. Acknowledgement: P. Panuzzo CNRS/Observatoire de Paris/PSL. 

Because of its exceptional nature, and to rule out the possibility that the solution is spurious, a confirmation of the result with several ground-based observatories was performed. The UVES spectrum for this system was obtained from the ESO archive, and follow-up observations were performed with the HERMES spectrograph in Spain and the SOPHIE spectrograph in France. The radial velocities obtained with these ground observatories complement Gaia’s radial velocities, which confirms the orbital solution derived from Gaia's data.
“Gaia is a true black hole detection machine because each of the three instruments can detect them”, says Laurent Eyer of Geneva Observatory, member of the Gaia Collaboration.

How did this black hole in the Milky Way originate?

Gaia’s photometry and spectra, as well as spectra obtained from ground-based observations with HERMES, SOPHIE and UVES, allow us to further unravel the secrets of this binary system. Since we cannot see the black hole, most of the information must be deduced from the companion star, which is a single old giant star. However, it is hard to determine the age of this ancient giant star. By comparing the colours and magnitude with theoretical models, it is estimated to be older than 11 billion years old.

From the companion star’s spectrum, it can be deduced that it has a low metallicity. This suggests that Gaia BH3 was also formed from a massive metal-poor star. Following the findings of the extra-galactic black hole population in this mass range from gravitational wave observations, it has been suggested that these high mass black holes are remnants of massive metal-poor stars. Gaia BH3 now provides support for this theory.

An intriguing companion

The star orbiting Gaia BH3 at about 16 times the Sun–Earth distance is rather uncommon: an ancient giant star, which formed in the first two billion years after the Big Bang, at the time our galaxy started to assemble. It belongs to the family of the Galactic stellar halo and is moving in the opposite direction to the stars of the Galactic disc. Its trajectory indicates that this star was probably part of a small galaxy, or a globular cluster, engulfed by our own galaxy more than eight billion years ago.

It supports, for the first time, the theory that the high-mass black holes observed by gravitational wave experiments were produced by the collapse of primeval massive stars poor in heavy elements. These early stars might have evolved differently from the massive stars we currently see in our galaxy.
The composition of the companion star can also shed light on the formation mechanism of this astonishing binary system. ”What strikes me is that the chemical composition of the companion is similar to what we find in old metal-poor stars in the galaxy,” explains Elisabetta Caffau, member of the Paris Observatory (CNRS), and  also a member of the Gaia collaboration.

For now, the formation process of this binary system with a black hole poses many questions. This new black hole challenges our understanding of how massive stars develop and evolve. Most theories predict that, as they age, massive stars shed a sizable part of their material through powerful winds; ultimately, they are partly blown into space when they explode as supernovas. What remains of their core further contracts to become either a neutron star or a black hole, depending on its mass. Cores large enough to end up as black holes of thirty times the mass of our Sun are very difficult to explain.

The companion star has very few elements heavier than hydrogen and helium, indicating that the massive star that became Gaia BH3 could also have been very poor in heavy elements. This is remarkable sinceit supports, for the first time, the theory that the high-mass black holes observed by gravitational wave experiments were produced by the collapse of primeval massive stars poor in heavy elements. These early stars might have evolved differently from the massive stars we currently see in our galaxy.

There are also many questions about where this black hole came from. Although it is currently in the plane of the Milky Way, its motion puts it in a retrograde orbit with a large inclination to the plane of the Milky Way. The black hole may come from a merger event of a small galaxy or a globular cluster merged with our Milky Way. It is expected that further studies will provide more insight on how Gaia BH3 ended up in the Milky Way.

This video shows the Galactic orbit of Gaia Black Hole 3 or Gaia BH3. It is an extract of the longer video. Credits: ESA/Gaia/DPAC- CC BY-SA 3.0 IGO. Acknowledgements: Video Animation: Stefan Jordan, Toni Sagristá with Gaia Sky - Text: Stefan Jordan, Pasquale Panuzzo, Ulrich Bastian, Tineke Roegiers, Berry Holl - Artificial voice - Based on "Discovery of a dormant 33 solar-masses black hole in pre-release Gaia astrometry" by Gaia Collaboration, et al., published in April 2024 in Astronomy & Astrophysics Letters.

“A growing number of black holes being found in the Milky Way with different methods, including the microlensing one reported in 2022 by OGLE and HST, brings us closer to obtaining a broader picture of the population of these objects in the Galaxy and may shed light on the nature of dark matter if an excess of these black holes is detected nearby.” says Łukasz Wyrzykowski, from Warsaw University in Poland and member of the Gaia Collaboration.

“From an observational point of view, discovering Gaia BH3 is not that hard, and specialized astronomical instruments will be able to detect its signatures as well. The difficulty is that you need to know which of the millions of stars to point your telescope at. This is where the power of a uniform all-sky survey like Gaia comes into play. Since Gaia observes all celestial sources that are bright enough to be seen by its detectors, we
were able to find the needle in the haystack,” says Johannes Sahlmann, member of the Gaia Science Operations Team at the European Space Astronomy Centre in Spain.
To date, Gaia data have only revealed the tip of the iceberg. Longer time spans of Gaia future data releases will undoubtedly reveal other binary systems containing black holes, but also exoplanets and other exotic binary systems. The Gaia Data Release (DR4) will be based on 5.5 years of observations, almost double the time period of the third data release, with about 3 years of observations. Currently, the full lifetime of Gaia is expected to be about 10.5 years.

Visualisation of the Gaia BH3 system showing its orbit and the motion of the system in our Galaxy. The video also describes the discovery in more detail. Credits: ESA/Gaia/DPAC- CC BY-SA 3.0 IGO. Acknowledgements: Video Animation: Stefan Jordan, Toni Sagristá with Gaia Sky - Text: Stefan Jordan, Pasquale Panuzzo, Ulrich Bastian, Tineke Roegiers, Berry Holl - Artificial voice - Based on "Discovery of a dormant 33 solar-masses black hole in pre-release Gaia astrometry" by Gaia Collaboration, et al., published in April 2024 in Astronomy & Astrophysics Letters. 

Reference article:
Gaia Collaboration; Panuzzo. P et al.«Discovery of a dormant 33 solar-mass black hole in pre-release Gaia astrometry». Astronomy & Astrophysics, April 2024. Doi: 10.1051/0004-6361/202449763
 

With 5,000 tiny robots in a mountaintop telescope, researchers can look 11 billion years into the past. The light from far-flung objects in space is just now reaching the Dark Energy Spectroscopic Instrument (DESI), a project managed by the Lawrence Berkeley National Laboratory (LBNL), enabling us to map our cosmos as it was in its youth and trace its growth to what we see today. Understanding how our universe has evolved is tied to how it ends, and to one of the biggest mysteries in physics: dark energy, the unknown ingredient causing our universe to expand faster and faster.

To study dark energy’s effects over the past 11 billion years, DESI has created the largest 3D map of our cosmos ever constructed, with the most precise measurements to date. This is the first time scientists have measured the expansion history of the young universe with a precision better than 1%, giving us our best view yet of how the universe evolved. Researchers shared the analysis of their first year of collected data in multiple papers that will be posted today on the arXiv and in talks at the American Physical Society meeting in the United States and the Rencontres de Moriond in Italy. These are the first 4th generation results on dark energy.  

 In this 360-degree video, take an interactive flight through millions of galaxies mapped using coordinate data from DESI. Credit: Fiske Planetarium, CU Boulder and DESI collaboration

“At the moment it looks like the first results from DESI are in agreement with the predictions of the current model”, said Hui Kong, postdoctoral researcher at IFAE, Barcelona, and  main author of one of the studies made public today. “There are some hints pointing at small temporal variations in the density of dark energy, but we will need more data to confirm them.”

Our leading model of the universe is known as Lambda CDM. It includes both a weakly interacting type of matter (cold dark matter, or CDM) and dark energy (Lambda). Both matter and dark energy shape how the universe expands – but in opposing ways. Matter and dark matter slow the expansion down, while dark energy speeds it up. The amount of each influences how our universe evolves. This model does a good job of describing results from previous experiments and how the universe looks throughout time.
 
However, when DESI’s first-year results are combined with data from other studies, there are some subtle differences with what Lambda CDM would predict. As DESI gathers more information during its five-year survey, these early results will become more precise, shedding light on whether the data are pointing to different explanations for the results we observe or the need to update our model. More data will also improve DESI’s other early results, which weigh in on the Hubble constant (a measure of how fast the universe is expanding today) and the mass of particles called neutrinos.  

“DESI, even with just the data from its first year, is already the spectroscopic survey with most collected data in the history and it goes on increasing this quantity with one million galaxies per month”, said Eusebio Sánchez, a researcher at CIEMAT, Madrid. “This amazing data sample makes possible to measure the expansion history of the Universe with an unprecedented precision. We are sure that DESI will increase our knowledge about the Universe and perhaps will allow us to make revolutionary discoveries”.
DESI’s overall precision on the expansion history across all 11 billion years is 0.5%, and the most distant epoch, covering 8-11 billion years in the past, has a record-setting precision of 0.82%. That measurement of our young universe is incredibly difficult to make. Yet within one year, DESI has become twice as powerful at measuring the expansion history at these early times as its predecessor (the Sloan Digital Sky Survey’s BOSS/eBOSS), which took more than a decade.

Traveling back in time

DESI is an international collaboration of more than 900 researchers from over 70 institutions around the world. The instrument was constructed and is operated with funding from the DOE Office of Science, and sits atop the U.S. National Science Foundation’s Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory, a program of NSF’s NOIRLab. 

Looking at DESI’s map, it’s easy to see the underlying structure of the universe: strands of galaxies clustered together, separated by voids with fewer objects. Our very early universe, well beyond DESI’s view, was quite different: a hot, dense soup of subatomic particles moving too 

fast to form stable matter like the atoms we know today. Among those particles were hydrogen and helium nuclei, collectively called baryons.

Tiny fluctuations in this early ionized plasma caused pressure waves, moving the baryons into a pattern of ripples that is similar to what you’d see if you tossed a handful of gravel into a pond. As the universe expanded and cooled, neutral atoms formed and the pressure waves stopped, freezing the ripples in three dimensions and increasing clustering of future galaxies in the dense areas. Billions of years later, we can still see this faint pattern of 3D ripples, or bubbles, in the characteristic separation of galaxies – a feature called Baryon Acoustic Oscillations (BAOs). 

Researchers use the BAO measurements as a cosmic ruler. By measuring the apparent size of these bubbles, they can determine distances to the matter responsible for this extremely faint pattern on the sky. Mapping the BAO bubbles both near and far lets researchers slice the data into chunks, measuring how fast the universe was expanding at each time in its past and modeling how dark energy affects that expansion.

This animation shows how baryon acoustic oscillations act as a cosmic ruler for measuring the expansion of the universe. Credit: Claire Lamman/DESI collaboration and Jenny Nuss/Berkeley Lab

“DESI is already more precise than all previous BAO surveys over the whole cosmic history”, said Violeta González Pérez, a researcher at the Theoretical Physics Department of the Universidad Autónoma from Madrid. “Its data allow us to study cosmic mysteries that lie beyond our current understanding of the Universe”.
Using galaxies to measure the expansion history and better understand dark energy is one technique, but it can only reach so far. At a certain point, light from typical galaxies is too faint, so researchers turn to quasars, extremely distant, bright galactic cores with black holes at their centers. Light from quasars is absorbed as it passes through intergalactic clouds of gas, enabling researchers to map the pockets of dense matter and use them the same way they use galaxies – a technique known as using the “Lyman-alpha forest.” 

“We use quasars as a backlight to basically see the shadow of the intervening gas between the quasars and us,” said Andreu Font-Ribera, a scientist at the Institute for High Energy Physics (IFAE) in Spain who co-leads DESI’s Lyman-alpha forest analysis. “It lets us look out further to when the universe was very young. It’s a really hard measurement to do, and very cool to see it succeed.”
 

Researchers used 450,000 quasars, the largest set ever collected for these Lyman-alpha forest measurements, to extend their BAO measurements all the way out to 11 billion years in the past. By the end of the survey, DESI plans to map 3 million quasars and 37 million galaxies.

State-of-the-art science

DESI is the first spectroscopic experiment to perform a fully “blinded analysis,” which conceals the true result from the scientists to avoid any subconscious confirmation bias. Researchers work in the dark with modified data, writing the code to analyze their findings. Once everything is finalized, they apply their analysis to the original data to reveal the actual answer.

"The fact that the analysis was carried out using data-blinding techniques provides us with an extra level of confidence in the results obtained," says Héctor Gil Marín, researcher at the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) and the Institut d’Estudis Espacials de Catalunya (IEEC). Blind analyses are already standard practice in fields such as experimental particle physics or clinical studies. Gil-Marín and other researchers at ICCUB have developed and implemented what turned out to be a very robust and difficult-to-decipher way to conceal the results of galaxy clustering in DESI until the analysis is completed. "We are confident that the extra effort involved in this will enhance the confidence and integrity of the DESI results," says Gil-Marín.

DESI’s data will be used to complement future sky surveys such as the Vera C. Rubin Observatory and Nancy Grace Roman Space Telescope, and to prepare for a potential upgrade to DESI (DESI-II) that was recommended in a recent report by the U.S. Particle Physics Project Prioritization Panel.

“It is exciting to see how the DESI results provide a precise view of how the Universe is” mentioned Francisco Javier Castander, a researcher of the Instituto de Ciencias del Espacio (ICE-CSIC) and the Institut d’Estudis Espacials de Catalunya (IEEC). “Moreover, this is only the beginning, with the new data we are gathering our measurements will be even more precise”.

DESI is supported by the DOE Office of Science and by the National Energy Research Scientific Computing Center, a DOE Office of Science user facility. Additional support for DESI is provided by the U.S. National Science Foundation; the Science and Technology Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the French Alternative Energies and Atomic Energy Commission (CEA); the National Council of Humanities, Sciences, and Technologies of Mexico; the Ministry of Science and Innovation of Spain; and by the DESI member institutions.

The DESI collaboration is honored to be permitted to conduct scientific research on Iolkam Du’ag (Kitt Peak), a mountain with particular significance to the Tohono O’odham Nation.

Spanish participant institutions in DESI include the Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), the Instituto de Ciencias del Espacio (ICE-CSIC), the Institut de Ciències del Cosmos de la Universitat de Barcelona (ICCUB), the Institut de Física d'Altes Energies (IFAE), the Instituto de Física Teórica (IFT - UAM/CSIC), the Instituto de Astrofísica de Andalucía (IAA) and the Instituto de Astrofísica de Canarias (IAC).
A complete list of participant institutions and more information about DESI is available in: https://www.desi.lbl.gov.

The Institute of Cosmos Sciences of the University of Barcelona proudly announces that five of its researchers have been awarded highly competitive fellowships from the "La Caixa" Foundation. 

The five distinguished recipients are Fotios Fronimos, Pau Solé, and Jéssica Gonçalves, who have been awarded INPhINIT doctoral fellowships, and Pablo Cano and Adrià Gómez, who have been granted Junior Leader postdoctoral fellowships.

”La Caixa” Foundation has awarded 105 new doctoral and postdoctoral scholarships to excellent researchers to carry out their projects at universities and research centers in Spain and Portugal. With the INPhINIT doctoral scholarships and the Junior Leader postdoctoral scholarships, the ”la Caixa” Foundation pursues the double objective of retaining and attracting talent to promote excellent research in these countries.

These scholarships offer competitive salaries and cross-training. In the case of doctoral programs, issues such as scientific communication, the emotional well-being of the researcher, leadership and funding opportunities are reinforced. In postdoctoral scholarships, an independent scientific career is promoted as an option for a professional future and innovation and leadership are encouraged.

Xavier Luri, Director of the Institute of Cosmos Sciences who also attended the ceremony, expressed his satisfaction in incorporating these five researchers at the institute, "The recognition of their talent and dedication by the 'La Caixa' Foundation is a testament to the exceptional quality of research being conducted at the Institute of Cosmos Sciences as a María de Maeztu Unit of Excellence." 

The Institute of Cosmos Sciences extends its heartfelt congratulations to Fotios Fronimos, Pau Solé, Jéssica Gonçalves, Pablo Cano, and Adrià Gómez on their well-deserved achievements. Their success not only reflects their individual excellence but also underscores the ICCUB's commitment to fostering a culture of scientific accomplishment.

For more information about the Institute of Cosmos Sciences at the University of Barcelona, please visit https://icc.ub.edu/.