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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.

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.

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

Gravitational-wave detectors such as LIGO, Virgo, and KAGRA are designed to measure minute distortions in space-time caused by violent cosmic events. The fourth observing run began in May 2023, and additional observations from the first half of the run (up to January 2024) will be published later in the summer.

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

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 at the GR-Amaldi meeting in Glasgow, Scotland, UK, July 14–18, 2025. The calibrated data used to detect and study GW231123 will be made available for other researchers to analyze through the Gravitational Wave Open Science Center (GWOSC).

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 the NSF with Germany (Max Planck Society), the UK (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 effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. Additional partners are listed at my.ligo.org/census.php.

The Virgo Collaboration is currently composed of approximately 880 members from 152 institutions in 17 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 Istituto Nazionale di Fisica Nucleare (INFN) in Italy, and the National Institute for Subatomic Physics (Nikhef) in the Netherlands. A list of the Virgo Collaboration groups can be found at: www.virgo-gw.eu/about/scientific-collaboration/. More information is available on the Virgo website at www.virgo-gw.eu.

KAGRA is the laser interferometer with 3-kilometer arm length in Kamioka, Gifu, Japan. The host institute is the 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 more than 400 members from 128 institutes in 17 countries/regions. KAGRA’s information for general audiences is at the website gwcenter.icrr.u-tokyo.ac.jp/en/. Resources for researchers are accessible from gwwiki.icrr.u-tokyo.ac.jp/JGWwiki/KAGRA.

In this study, researcher developed a new imaging approach that combines two powerful techniques to solve this problem. First, a special type of microscope called a two-photon microscope is used, which can look deep into live tissues with minimal damage. To improve how steady the tissue remains during imaging, they designed a custom-made, 3D-printed holder that gently uses suction to hold the tissue in place. This suction-based stabilization helps keep the tissue still within the camera’s focus, which is essential when trying to capture high-resolution images of tiny moving structures.

Next, the images are improved further using advanced computer algorithms. These included techniques to reduce “noise” (unwanted blurry spots in images), correct for tiny shifts or drifts in the picture, and enhance image sharpness using a method called Super-Resolution Radial Fluctuations (SRRF). Together, these improvements doubled the resolution, allowing the researchers to clearly see details smaller than 250 nanometers, far beyond what a typical microscope can do.

To demonstrate the power of this approach, they used a genetically modified mouse called the Mito-Dendra2 model, where mitochondria glow green under the microscope. With this model, the team was able to watch, in real time, how mitochondria split, merge, move, and respond to different health conditions. For example, it is observed how mitochondria behave in a model of alcohol-induced liver disease, and how a natural compound called berberine can help restore mitochondrial health during recovery. These insights would be nearly impossible to gain without being able to see the mitochondria directly inside a living animal.

This work is important because it allows scientists to study the smallest building blocks of life in their most natural environment, inside living and functioning tissue. The combination of gentle physical stabilization, powerful microscopy, and advanced image processing offers a new standard for intravital imaging within live organisms. It opens the door for new discoveries in how cells respond to stress, how diseases develop, and how treatments work at the organelle level. In short, this breakthrough provides researchers with a valuable tool to explore the hidden world inside living tissues, making it easier to understand life at the cellular level and develop better ways to diagnose and treat disease.

The research group of Prof. Jun Ki Kim from Asan Medical Center, the largest hospital in Korea, and University of Ulsan, College of Medicine, introduces a groundbreaking technology that provides super-resolution imaging inside the cells of living animals. Located at the intersection of engineering, medicine, and optics, the work conducted in this optics laboratory within a biomedical engineering department and affiliated medical center plays a vital role in shaping the future of healthcare and scientific discovery. This interdisciplinary environment brings together physicists, engineers, biologists, and clinicians to address some of the most pressing challenges in modern medicine-diagnosing diseases earlier, treating them more precisely, and understanding human biology at a deeper level.

The importance of this work lies in its focus on translating light-based technologies: such as advanced imaging systems, diagnostic tools, and therapeutic devices, into real-world clinical solutions. In hospitals and clinics, doctors often rely on indirect indicators of disease, like blood tests or tissue biopsies, which can be invasive or limited in detail. Optical technologies offer a different approach: they provide real-time, non-invasive insight into the human body, revealing structures and molecular changes that are invisible to the naked eye.

In this lab, researchers develop tools that can image cells inside a living body, detect early signs of disease, or guide surgeons during operations with light-based visualization techniques. Working hand-in-hand with medical professionals, engineers transform scientific principles into devices that are practical, safe, and effective for patient care.

Moreover, the lab’s presence within a medical center fosters rapid collaboration and translation. Research does not remain confined to the lab bench; instead, it moves efficiently toward patient trials and clinical use. This dynamic setting ensures that innovations are not only technically advanced but also medically relevant. In the broader context, this work contributes to a global effort to make medicine more personalized, less invasive, and more data-driven and ultimately improving outcomes and quality of life for patients around the world.

The research group specializes in the development and application of advanced bio-optical imaging systems, focusing on cutting-edge technologies that enable the visualization and analysis of biological tissues at cellular and subcellular levels. Their work in in vivo microscopy allows for high-resolution imaging of living tissues, providing critical insights into dynamic biological processes in real-time. This technique is particularly valuable in studying tissue structures and identifying disease markers, offering significant potential for improving diagnostics and therapeutic interventions.

Another major area of focus for the group is medical device development, where they design and create innovative tools that integrate optical and imaging technologies for clinical applications. Their efforts are aimed at enhancing the precision, reliability, and accessibility of diagnostic devices, ensuring that they meet the needs of both healthcare providers and patients. In parallel, the group is heavily involved in the development of optical probes that can be used for in-depth, non-invasive tissue analysis. These probes are designed to interact with biological tissues at the molecular level, enabling detailed, real-time assessments of cellular processes.

A key area of the group’s research is diagnosis and therapy, particularly leveraging the power of Raman spectroscopy. By utilizing the unique vibrational properties of molecules, Raman spectroscopy provides a powerful tool for identifying chemical signatures associated with various diseases, enabling early detection and precise monitoring of therapeutic responses. This approach holds great promise for improving disease diagnosis, particularly in oncology and other fields where early intervention is critical.

Through their multidisciplinary work, the research group is advancing the frontiers of medical diagnostics, offering new solutions for in vivo imaging, disease detection, and personalized therapy.

What started as a student field trip along the cliffs of Dorset turned into the discovery of a new prehistoric species. A 16.5-millimeter lower jaw, embedded in rock near Swanage, is now reshaping how scientists view early mammal evolution.

The discovery was made by an undergraduate student from the University of Portsmouth. The fossil belongs to a type of extinct mammal called a multituberculate.

These small, rodent-like creatures once lived alongside dinosaurs and were known for their distinctively complex teeth.

A curious jaw, a surprising species

The fossil was uncovered at Durlston Bay, a site famous for its rich geological layers. It’s the first multituberculate jaw found there since the 1800s.

Though it looks a bit like a rabbit’s jaw at first glance, the structure of the teeth tells a different story. A sharp incisor juts out at the front, followed by a gap, and then four blade-like premolars.

“I instantly had my suspicions of what the jaw was when I found it at the beach, but couldn’t have imagined where the discovery would take me,” said Ben Weston, an undergraduate paleontology student.

“I’m extremely grateful to the team and to the university for helping me take my first steps into academic paleontology.”

Researchers at the University of Portsmouth confirmed that the fossil is from a species that had never been identified before.

Technology brings the fossil to life

The fossil wasn’t easy to examine. Rock still clung to key parts of the specimen. To get around this, the team turned to high-resolution CT scanning.

Dr. Charles Wood, a senior scientific officer at the university, scanned the fossil, allowing scientists to see inside the rock without damaging the sample.

Jake Keane, a former Portsmouth paleontology student now working in Abu Dhabi, helped process the scans. In just a few hours, he digitally removed the surrounding rock and isolated the teeth in fine detail.

The scans were then turned into 3D-printed models by John Fearnly, lead technician in the university’s Faculty of Technology. These models were ten times larger than the original, making it safer and easier to study the fossil in depth.

New mammal gets a name

The team named the new species Novaculadon mirabilis. “Novacula” means razor, a nod to its sharp back teeth. “Mirabilis” refers to the jaw’s almost perfect preservation.

Portsmouth student Hamzah Imran created an artistic rendering of the animal. It’s imagined as a small, furry creature with a mix of spots and stripes – though its actual appearance remains speculative.

Based on its teeth, Novaculadon mirabilis likely ate insects and other small invertebrates. Its slicing premolars and pointed incisors set it apart from modern rodents like rats or squirrels.

A hotspot for new mammal species

This isn’t the first time a student has made a big find in the same area. In 2017, another Portsmouth undergraduate, Grant Smith, discovered fossils of two new mammal species thought to be among humanity’s earliest relatives.

Dr. Steve Sweetman, a researcher at the University of Portsmouth, also worked on this new discovery.

“This is a remarkable find that reminds me of when Grant found those extraordinary eutherian mammal teeth,” said Dr. Sweetman.

“When I first saw Grant’s specimens, my jaw dropped – and I had exactly the same reaction to Ben’s multituberculate jaw. It’s incredible that Durlston Bay keeps delivering such significant mammal discoveries by our undergraduate students.”

Evolution insights from tiny jaw

Beyond the scientific importance, the discovery highlights the value of collaborative research.

“Looking back now that the discovery has been published, I am amazed at how many people it took to describe this little mammal,” said Professor David Martill.

“I especially appreciated that all team members were University staff or present and former students – a true team effort including academics, technicians, alumni, and students with diverse talents across three departments.”

The fossil helps researchers better understand how early mammals survived during the age of dinosaurs. While multituberculates lived through the mass extinction that wiped out dinosaurs, they eventually died out during the Oligocene, around 33 million years ago.

With over 200 known species, multituberculates were the most diverse group of mammals in the Mesozoic era. They filled many ecological roles – some burrowed, others climbed trees. This new discovery adds to what we know about their evolution and survival.

And it serves as a reminder that major scientific contributions can come from anyone – even a 22-year-old student on a windy beach in Dorset.

Image Credit: Hamzah Imran

The full study was published in the journal Proceedings of the Geologists Association.

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