Astronomy

GW231123: LIGO-Virgo-KAGRA detect most massive black hole merger to date

By ScientifiCult 14 July 2025

GW231123: LIGO-Virgo-KAGRA detect most massive black hole merger to date

Gravitational waves from massive black holes challenge current astrophysical models

The LIGO-Virgo-KAGRA (LVK) Collaboration has detected the merger of the most massive black holes ever observed with gravitational waves using the US National Science Foundation (NSF)-funded LIGO observatories. The powerful merger produced a final black hole approximately 225 times the mass of our Sun. The signal, designated GW231123, was detected during the fourth observing run of the LVK network on November 23, 2023.

The two black holes that merged were approximately 103 and 137 times the mass of the Sun. In addition to their high masses they are also rapidly spinning, making this a uniquely challenging signal to interpret and suggesting the possibility of a complex formation history.

“The discovery of such a massive and highly spinning system presents a challenge not only to our data analysis techniques – says Ed Porter, researcher at the Astroparticle and Cosmology laboratory (APC) of CNRS in Paris – but will have a major effect on the theoretical studies of black hole formation channels and waveform modelling for many years to come. Actually, current models of stellar evolution do not allow the existence of such massive black holes, which could possibly have formed through previous mergers of smaller black holes.”

Approximately 100 black-hole mergers have previously been observed through gravitational waves, analysed and shared with the wider scientific community. Until now the most massive binary was the source of GW190521, with a much smaller total mass of “only” 140 times that of the sun.

Before now, the most massive black hole merger—produced by an event that took place in 2021 called GW190521—had a total mass of 140 times that of the Sun.

In the more recent GW231123 event, the 225-solar-mass black hole was created by the coalescence of black holes each approximately 100 and 140 times the mass of the Sun.

In addition to their high masses, the black holes are also rapidly spinning.

“This is the most massive black hole binary we’ve observed through gravitational waves, and it presents a real challenge to our understanding of black hole formation,” says Mark Hannam of Cardiff University and a member of the LVK Collaboration. “Black holes this massive are forbidden through standard stellar evolution models. One possibility is that the two black holes in this binary formed through earlier mergers of smaller black holes.”

Dave Reitze, the executive director of LIGO at Caltech, says, “This observation once again demonstrates how gravitational waves are uniquely revealing the fundamental and exotic nature of black holes throughout the universe.”

A record-breaking system

The high mass and extremely rapid spinning of the black holes in GW231123 push the limits of both gravitational-wave detection technology and current theoretical models. Extracting accurate information from the signal required the use of models that account for the intricate dynamics of highly spinning black holes.

“The black holes appear to be spinning very rapidly—near the limit allowed by Einstein’s theory of general relativity,” explains Charlie Hoy of the University of Portsmouth and a member of the LVK. “That makes the signal difficult to model and interpret. It’s an excellent case study for pushing forward the development of our theoretical tools.”

Researchers are continuing to refine their analysis and improve the models used to interpret such extreme events. “It will take years for the community to fully unravel this intricate signal pattern and all its implications,” says Gregorio Carullo of the University of Birmingham and a member of the LVK. “Despite the most likely explanation remaining a black hole merger, more complex scenarios could be the key to deciphering its unexpected features. Exciting times ahead!”

Probing the limits of gravitational-wave astronomy

The high mass and extremely rapid spinning of the black holes in GW231123 pushes the limits of both gravitational-wave detection technology and current theoretical models. Extracting accurate information from the signal required the use of theoretical models that account for the complex dynamics of highly spinning black holes.

“This event pushes our instrumentation and data-analysis capabilities to the edge of what’s currently possible,” says Dr. Sophie Bini, a postdoctoral researcher at Caltech, previously at the University of Trento. “It’s a powerful example of how much we can learn from gravitational-wave astronomy—and how much more there is to uncover.”

Gravitational-wave detectors such as LIGO in the United States, Virgo in Italy, and KAGRA in Japan are designed to measure minute distortions in spacetime caused by violent cosmic events like black hole mergers. The fourth observing run began in May 2023 and observations from the first half of the run (up to January 2024) will be published later in the summer.

“With the longest continuous observation to date and enhanced sensitivity, the LIGO-Virgo-KAGRA fourth observing campaign is delivering invaluable new insights into our understanding of the universe –says Viola Sordini, researcher at the Institute of Physics of the 2 Infinities (IP2I) of CNRS in Lyon and deputy spokesperson of the Virgo Collaboration – This exciting discovery opens a new season of results, with many more expected throughout the summer and a continued stream of findings anticipated over the next two years. Publications are followed by release of the data, in support of the broader scientific community and open science”

GW231123 will be presented at the 24th International Conference on General Relativity and Gravitation (GR24) and the 16th Edoardo Amaldi Conference on Gravitational Waves, held jointly as the GR-Amaldi meeting in Glasgow, UK, from July 14-18 2025.

LIGO, the Laser Interferometer Gravitational-wave Observatory, made history in 2015 when it made the first-ever direct detection of gravitational waves, ripples in space-time. In that case, the waves emanated from a black hole merger that resulted in a final black hole 62 times the mass of our Sun. The signal was detected jointly by the twin detectors of LIGO, one located in Livingston, Louisiana, and the other in Hanford, Washington.

Since then, the LIGO team has teamed up with partners at the Virgo detector in Italy and KAGRA (Kamioka Gravitational Wave Detector) in Japan to form the LVK Collaboration. These detectors have collectively observed more than 200 black hole mergers in their fourth run, and about 300 in total since the start of the first run in 2015.

The LIGO-Virgo-KAGRA Collaboration

LIGO is funded by the NSF, and operated by Caltech and MIT, which conceived and built the project. Financial support for the Advanced LIGO project was led by NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council) making signiﬁcant commitments and contributions to the project. More than 1,600 scientists from around the world participate in the eQort through the LIGO Scientiﬁc Collaboration, which includes the GEO Collaboration. Additional partners are listed at https://my.ligo.org/census.php.

The Virgo Collaboration is currently composed of approximately 1.000 members from 175 institutions in 20 different (mainly European) countries. The European Gravitational Observatory (EGO) hosts the Virgo detector near Pisa in Italy, and is funded by Centre National de la Recherche Scientifique (CNRS) in France, the National Institute of Nuclear Physics (INFN) in Italy, the National Institute of Subatomic Physics (Nikhef) in the Netherlands, The Research Foundation – Flanders (FWO) e the Belgian Fund for Scientific Research (F.R.S.–FNRS). A list of the Virgo Collaboration groups can be found at: https://www.virgo-gw.eu/about/scientiﬁc-collaboration/. More information is available on the Virgo website at https://www.virgo-gw.eu.

KAGRA is the laser interferometer with 3 km arm-length in Kamioka, Gifu, Japan. The host institute is Institute for Cosmic Ray Research (ICRR), the University of Tokyo, and the project is co-hosted by National Astronomical Observatory of Japan (NAOJ) and High Energy Accelerator Research Organization (KEK). KAGRA collaboration is composed of over 400 members from 128 institutes in 17 countries/regions. KAGRA’s information for general audiences is at the website https://gwcenter.icrr.u-tokyo.ac.jp/en/. Resources for researchers are accessible from http://gwwiki.icrr.u-tokyo.ac.jp/JGWwiki/KAGRA.

Press release from EGO and California Institute of Technology

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Astronomy

Webb captures evidence of a lightweight planet around TWA 7

By ScientifiCult 25 June 2025

Webb captures evidence of a lightweight planet around TWA 7

Astronomers using the NASA/ESA/CSA James Webb Space Telescope have captured compelling evidence of a planet with a mass similar to Saturn orbiting the young nearby star TWA 7. If confirmed, this would represent Webb’s first direct image discovery of a planet, and the lightest planet ever seen with this technique.

The international team, led by Dr. Anne-Marie Lagrange, CNRS researcher at the Observatoire de Paris-PSL and Université Grenoble Alpes in France, detected a faint infrared source in the disc of debris surrounding TWA 7 using JWST’s Mid-Infrared Instrument (MIRI) and its coronagraph. The source is located about 1.5 arcseconds from the star on the sky which, at the distance of TWA7, is roughly fifty times the distance of the Earth to the Sun. This matches the expected position of a planet that would explain key features seen in the debris disc.

Using the coronagraph on Webb’s Mid-Infrared Instrument (MIRI) on 21 June 2024, the team carefully suppressed the bright glare of the host star to reveal faint nearby objects. This technique, called high-contrast imaging, enables astronomers to directly detect planets that would otherwise be lost in the overwhelming light from their host star. After subtracting residual starlight using advanced image processing, a faint infrared source was revealed near TWA 7, distinguishable from background galaxies or Solar System objects. The source is located in a gap in one of three dust rings that were discovered around TWA 7 by previous ground-based observations. Its brightness, colour, distance from the star, and position within the ring are consistent with theoretical predictions for a young, cold, Saturn-mass planet sculpting the surrounding debris disc.

“Our observations reveal a strong candidate for a planet shaping the structure of the TWA 7 debris disc, and its position is exactly where we expected to find a planet of this mass,” said Dr. Lagrange.

“This observatory enables us to capture images of planets with masses similar to those in the solar system, which represents an exciting step forward in our understanding of planetary systems, including our own,”

added co-author Mathilde Malin of Johns Hopkins University and the Space Telescope Science Institute in Baltimore.

Initial analysis suggests that the object — referred to as TWA 7b — could be a young, cold planet with a mass around 0.3 times that of Jupiter (~100 Earth masses) and a temperature near 320 Kelvin (roughly 47 degrees Celsius). Its location aligns with a gap in the disc, hinting at a dynamic interaction between the planet and its surroundings.

Debris discs filled with dust and rocky material are found around both young and older stars, although they are more easily detected around younger stars as they are brighter. They often feature visible rings or gaps, thought to be created by planets that have formed around the star, but such a planet has yet to be detected within a debris disc. Once verified, this discovery would mark the first time a planet has been directly associated with sculpting a debris disc and could offer the first observational hint of a trojan disc — a collection of dust trapped in the planet’s orbit.

TWA 7, also known as CE Antliae, is a young (~6.4 million years old) M-type star located about 111 light-years away in the TW Hydrae association. Its nearly face-on disc made it an ideal target for Webb’s high-sensitivity mid-infrared observations.

The findings highlight Webb’s ability to explore previously unseen, low-mass planets around nearby stars. Ongoing and future observations will aim to better constrain the properties of the candidate, verify its planetary status, and deepen our understanding of planet formation and disc evolution in young systems.This preliminary result showcases the exciting new frontier that JWST is opening for exoplanet discovery and characterisation.

These observations were taken as part of the Webb observing programme #3662. The results have been published today in Nature.

An image of a nearby star and its vicinity. The star itself has been blocked out and its bright light has been removed. A dashed circle with a star symbol at the centre of the image marks the star’s location. A fuzzy blue disc surrounds the star. An orange spot, near to the star and inside this disc, is identified as a planet orbiting the star. A fainter orange spot far from the centre marks a distant star. — Astronomers using the NASA/ESA/CSA James Webb Space Telescope have captured compelling evidence of a planet with a mass similar to Saturn orbiting the young nearby star TWA 7. If confirmed, this would represent Webb’s first direct image discovery of a planet, and the lightest planet ever seen with this technique. Using the coronagraph on Webb’s Mid-Infrared Instrument (MIRI) on 21 June 2024, the team carefully suppressed the bright glare of the host star to reveal faint nearby objects. This technique, called high-contrast imaging, enables astronomers to directly detect planets that would otherwise be lost in the overwhelming light from their host star. After subtracting residual starlight using advanced image processing, a faint infrared source was revealed near TWA 7, distinguishable from background galaxies or Solar System objects. The source is located in a gap in one of three dust rings that were discovered around TWA 7 by previous ground-based observations. Its brightness, colour, distance from the star, and position within the ring are consistent with theoretical predictions for a young, cold, Saturn-mass planet sculpting the surrounding debris disc. Initial analysis suggests that the object — referred to as TWA 7b — could be a young, cold planet with a mass around 0.3 times that of Jupiter (~100 Earth masses) and a temperature near 320 Kelvin (roughly 47 degrees Celsius). In this image from MIRI, light from the star TWA 7 has been subtracted. The location of the star is marked with a circle and a star symbol at the centre of the image. This leaves light from the debris disc around the star, as well as other infrared sources, visible. The bright spot to the upper right of the star is the source identified as TWA 7b, within the debris disc. The more distant orange spot visible in the left of the image is an unrelated background star. Only a single MIRI band was used in this image (seen here in orange). The blue colour visible in the image results from an additional band taken by the SPHERE instrument of ESO’s Very Large Telescope (VLT), which showcases the location of the disc surrounding the host star and the exoplanet creating a gap within the disc that is revealed by MIRI.
Credit: ESA/Webb, NASA, CSA, A.M. Lagrange, M. Zamani (ESA/Webb)

Bibliographic information:

Lagrange, AM., Wilkinson, C., Mâlin, M. et al. Evidence for a sub-Jovian planet in the young TWA 7 disk, Nature (2025), DOI: https://doi.org/10.1038/s41586-025-09150-4

Press release from ESA Webb.

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Genetics

Using paleogenomics to elucidate 10,000 years of immune system evolution

By ScientifiCult 13 January 2023

Using paleogenomics to elucidate 10,000 years of immune system evolution

Scientists from the Institut Pasteur, Université Paris Cité, the CNRS and the Collège de France have used paleogenomics to trace 10,000 years of human immune system evolution. They analyzed the genomes of more than 2,800 individuals who lived in Europe over the past ten millennia. They were able to date the increase in frequency of most of the mutations that are advantageous in defending against pathogens to after the Bronze Age, 4,500 years ago. The scientists also observed that mutations conferring a higher risk of developing inflammatory disorders have become more frequent over the past 10,000 years. These enlightening results on the effects of natural selection on immunity genes were published in the journal Cell Genomics on January 13, 2023.

In the 1950s, the geneticist J.B.S. Haldane attributed the maintenance or persistence of the mutation responsible for anomalies in red blood cells commonly observed in Africa to the protection these anomalies provided against malaria, an endemic infection that claims millions of lives. This theory suggested that pathogens are among the strongest selective pressures faced by humans. Several population genetics studies subsequently confirmed the theory. But major questions remained, especially regarding the specific epochs during which the selective pressures exerted by pathogens on human populations were strongest and their impact on the present-day risk of developing inflammatory or autoimmune disorders.

To address these questions, scientists from the Institut Pasteur, Université Paris Cité, the CNRS and the Collège de France, in collaboration with the Imagine Institute and The Rockefeller University (United States), adopted an approach based on paleogenomics. This discipline, which studies the DNA from fossil remains, has led to major discoveries about the history and evolution of humans and human diseases, as illustrated by the decision to award the 2022 Nobel Prize in Physiology or Medicine to the paleogeneticist Svante Pääbo. In the study led by the Institut Pasteur, published on January 13 in the journal Cell Genomics, the scientists analyzed the variability of the genomes of more than 2,800 individuals who lived in Europe over the past ten millennia – a period covering the Neolithic, the Bronze Age, the Iron Age, the Middle Ages and the present.

By reconstituting the evolution over time of hundreds of thousands of genetic mutations, the scientists initially identified mutations that rapidly increased in frequency in Europe, indicating that they were advantageous. These mutations that evolved under “positive” natural selection are mainly located in 89 genes enriched in functions relating to the innate immune response, including especially the OAS genes – which are responsible for antiviral activity – and the gene responsible for the ABO blood group system. Surprisingly, most of these positive selection events, which demonstrate a genetic adaptation to the pathogenic environment, began recently, from the start of the Bronze Age, around 4,500 years ago. The scientists explain this “acceleration” in adaptation by the growth in the human population during this period and/or by strong selective pressures exerted by pathogens in the Bronze Age, probably linked to the spread of severe infectious diseases such as plague.

At the same time, the scientists also looked at the opposite situation, in other words, mutations whose frequency fell significantly over the past ten millennia. These mutations are probably subject to “negative” selection because they increase the risk of disease. They noted that once again, these selection events mainly began in the Bronze Age. Many of these disadvantageous mutations were also located in genes associated with the innate immune response, such as TYK2, LPB, TLR3 and IL23R, and have been confirmed in experimental research to have a deleterious effect in terms of infectious disease risk. The results emphasize the value of adopting an evolutionary approach in research on genetic susceptibility to infectious diseases.

Finally, the scientists explored the theory that the selection exerted by pathogens in the past gave an advantage to alleles conferring resistance to infectious diseases, but that in turn these alleles have increased the present-day risk of autoimmune or inflammatory disorders. They investigated the few thousand mutations known to increase susceptibility firstly to tuberculosis, hepatitis, HIV or COVID-19, and secondly to rheumatoid arthritis, systemic lupus erythematosus or inflammatory bowel disease. By looking at the evolution of these mutations over time, they observed that those associated with an increased risk of inflammatory disorders – including Crohn’s disease – became more frequent over the past 10,000 years, while the frequency of those associated with a risk of developing infectious diseases decreased.

“These results suggest that the risk of inflammatory disorders has increased in Europeans since the Neolithic period because of a positive selection of mutations improving resistance to infectious diseases,”

explains Lluis Quintana-Murci, director of the study and Head of the Human Evolutionary Genetics Unit (Institut Pasteur/CNRS Evolutionary Genomics, Modeling and Health Unit/Université Paris Cité).

The results of the study, which harnessed the huge potential of paleogenomics, show that natural selection has targeted human immunity genes over the past ten millennia in Europe, especially since the start of the Bronze Age, and contributed to present-day disparities in terms of the risk of infectious and inflammatory diseases.

As well as the institutions mentioned above, this research was supported by the French Foundation for Medical Research (FRM), the Allianz-Institut de France Foundation and the Fondation de France.

Bibliographic information:

Genetic adaptation to pathogens and increased risk of inflammatory disorders in post-Neolithic Europe, Cell Genomics, January 13, 2023

Press release from Institut Pasteur

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