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In a cosmic event that defies current scientific understanding, astronomers have confirmed the most massive black hole merger ever recorded.

Using gravitational waves – ripples in the fabric of spacetime – the LIGO-Virgo-KAGRA (LVK) Collaboration observed two enormous black holes crashing together to form a single, ultra-massive entity over 225 times the mass of the Sun.

This record-breaking discovery not only challenges existing theories of how black holes form and evolve but also marks a significant leap forward for gravitational-wave astronomy.

Detected initially on 23 November 2023, and dubbed GW231123, the signal is already reshaping the way scientists think about the most extreme objects in the Universe.

The data was captured by the U.S. National Science Foundation-funded LIGO detectors in Hanford and Livingston, with vital contributions from Virgo in Italy and KAGRA in Japan.

Global collaboration powers discovery

The LIGO-Virgo-KAGRA Collaboration is a massive international effort involving over 2,000 scientists from more than 300 institutions worldwide.

Each observatory contributes unique technological strengths:

• LIGO, operated by Caltech and MIT, is supported by the U.S. NSF and international partners.
• Virgo, located in Italy, is operated by the European Gravitational Observatory and funded by research agencies across Europe.
• KAGRA, in Japan, is hosted by the University of Tokyo’s Institute for Cosmic Ray Research and co-managed by major Japanese scientific institutions.

These facilities form a globally distributed observatory capable of triangulating cosmic events with exceptional precision.

Breaking boundaries of stellar evolution

What makes GW231123 particularly puzzling is not just its sheer scale, but also the intense spin of the merging black holes.

Rapid rotation and unusually high mass suggest a complex formation history, likely involving prior black hole merger, an evolutionary pathway that current models don’t readily explain.

Traditional theories of stellar evolution predict an upper limit for black hole masses formed from dying stars.

These new observations push far beyond those limits, compelling astrophysicists to reconsider how such supermassive objects might arise.

Theories involving hierarchical mergers – successive collisions and fusions of smaller black holes – are gaining traction as a possible explanation.

Gravitational-wave detection at its limits

GW231123 not only sets a new benchmark for mass but also pushes the technological and analytical limits of gravitational-wave astronomy.

Accurately interpreting the signal required advanced modelling that accounts for the chaotic behaviour of spinning black holes – a feat that would have been impossible just a few years ago.

This event demonstrates the extraordinary capabilities of next-generation gravitational-wave detectors. The fourth observing run, which began in May 2023, features the longest and most sensitive observation campaign to date.

Results from the first half of this run are expected to be published later this summer, with many more discoveries anticipated through 2026.

A new era for black hole astronomy

GW231123 surpasses the previous heavyweight record-holder, GW190521, which involved black holes with a combined mass of 140 solar masses.

With over 100 black hole mergers now catalogued since the first detection in 2015, each new event adds vital pieces to the cosmic puzzle.

This particular black merger is a turning point, offering new insights into the lifecycle of massive celestial bodies and the nature of spacetime itself.

It underscores the need for evolving theoretical frameworks and more sophisticated models of how black holes form, grow, and interact.

Open data and deeper insights

The LVK Collaboration continues to support open science by releasing data after publication, enabling broader scientific analysis and accelerating discovery.

GW231123 will be showcased this week at the GR-Amaldi 2025 conference in Glasgow, where researchers will discuss the profound implications of this find.

As gravitational-wave observatories grow more sensitive and analytical methods become more refined, we can expect even deeper insights into the most extreme phenomena in the Universe.

If you happen to find yourself in the Southern Hemisphere with binoculars and a good view of the night sky on a dark and clear summer night, you might just be able to spot the Sculptor galaxy. And if your eyes were prisms that could separate light into the thousands of colors making it up, then congratulations: After hours of staring, you could have recreated the newest image of one of the nearest neighbors to our Milky Way galaxy.

This is not just another stunningly gorgeous picture of a nearby galaxy. Because it reveals the type of light coming from each location in the galaxy, this image of the Sculptor galaxy is a treasure trove of information that astronomers around the world cannot wait to pick apart.

As an astronomy Ph.D. student at Ohio State University, I (Rebecca) am one of the lucky people who gets to stare at this image for hours every day, alongside my adviser (Adam), discovering meaning behind the beauty everyone can appreciate.

Creating the image

The Sculptor galaxy lies 11 million light-years from the Milky Way. This may sound unfathomably far, but it actually makes Sculptor one of the closest galaxies to Earth.

For this reason, Sculptor has been the primary target for many observations. In 2022, an international team of scientists observed Sculptor with the Multi-Unit Spectroscopic Explorer, MUSE, on the European Southern Observatory’s Very Large Telescope in Chile, and publicly released the data this June.

Most astronomical observations obtain either an image of a single color of light – for example, red or blue – or a spectrum, which splits the light coming from the whole galaxy into many different colors.

MUSE, conveniently, does both, producing a spectrum at every location it observes. One observation creates thousands of images in thousands of colors, each tracing the critical components that make up the galaxy: stars, dust and gas.

It may look like only one picture, but this image of Sculptor is actually over 100 individual observations and 8 million individual spectra, painstakingly stitched together to reveal millions of stars all in one cohesive galaxy.

Scientific significance

The light associated with the stars in Sculptor is colored white, and gas made up of charged particles is colored red. The largest concentration of both is found in the spiral arms. At the very center of the galaxy is a nuclear starburst: a region of extreme star formation that is blowing material out of the galaxy.

There is even information in the absence of light. Dust obscures light emitted from behind it, creating a shadow effect called dust lanes. Tracing these dust lanes reveals the cold, dense material that exists between stars. Scientists believe this dark material is the fuel that will form the next generation of stars.

There is a lot to look at in this image, but the subject of my work and what I find most interesting is the gas illuminated in red. In these star-forming regions, young and massive stars excite the gas around them, which then glows with a specific color to reveal the chemical makeup and physical conditions of the gas.

This image represents one of the first times that astronomers have obtained images of thousands of star-forming regions at this impressive level of detail. A component of our team’s research uses the data from MUSE to understand how these regions are structured and how they interact with the surrounding galaxy.

By meticulously piecing all of this information together, astronomers can use this image to learn more about the formation and evolution of stars across the universe.

Our first meeting was a bit awkward. One of us is an archaeologist who studies how past peoples interacted with their environments. Two of us are geophysicists who investigate interactions between solar activity and Earth’s magnetic field.

When we first got together, we wondered whether our unconventional project, linking space weather and human behavior, could actually bridge such a vast disciplinary divide. Now, two years on, we believe the payoffs – personal, professional and scientific – were well worth the initial discomfort.

Our collaboration, which culminated in a recent paper in the journal Science Advances, began with a single question: What happened to life on Earth when the planet’s magnetic field nearly collapsed roughly 41,000 years ago?

Weirdness when Earth’s magnetic shield falters

This near-collapse is known as the Laschamps Excursion, a brief but extreme geomagnetic event named for the volcanic fields in France where it was first identified. At the time of the Laschamps Excursion, near the end of the Pleistocene epoch, Earth’s magnetic poles didn’t reverse as they do every few hundred thousand years. Instead, they wandered, erratically and rapidly, over thousands of miles. At the same time, the strength of the magnetic field dropped to less than 10% of its modern day intensity.

So, instead of behaving like a stable bar magnet – a dipole – as it usually does, the Earth’s magnetic field fractured into multiple weak poles across the planet. As a result, the protective force field scientists call the magnetosphere became distorted and leaky.

The magnetosphere normally deflects much of the solar wind and harmful ultraviolet radiation that would otherwise reach Earth’s surface.

So, during the Laschamps Excursion when the magnetosphere broke down, our models suggest a number of near-Earth effects. While there is still work to be done to precisely characterize these effects, we do know they included auroras – normally seen only in skies near the poles as the Northern Lights or Southern Lights – wandering toward the equator, and significantly higher-than-present-day doses of harmful solar radiation.

The skies 41,000 years ago may have been both spectacular and threatening. When we realized this, we two geophysicists wanted to know whether this could have affected people living at the time.

The archaeologist’s answer was absolutely.

Human responses to ancient space weather

For people on the ground at that time, auroras may have been the most immediate and striking effect, perhaps inspiring awe, fear, ritual behavior or something else entirely. But the archaeological record is notoriously limited in its ability to capture these kinds of cognitive or emotional responses.

Researchers are on firmer ground when it comes to the physiological impacts of increased UV radiation. With the weakened magnetic field, more harmful radiation would have reached Earth’s surface, elevating risk of sunburn, eye damage, birth defects, and other health issues.

In response, people may have adopted practical measures: spending more time in caves, producing tailored clothing for better coverage, or applying mineral pigment “sunscreen” made of ochre to their skin. As we describe in our recent paper, the frequency of these behaviors indeed appears to have increased across parts of Europe, where effects of the Laschamps Excursion were pronounced and prolonged.

At this time, both Neanderthals and members of our species, Homo sapiens, were living in Europe, though their geographic distributions likely overlapped only in certain regions. The archaeological record suggests that different populations exhibited distinct approaches to environmental challenges, with some groups perhaps more reliant on shelter or material culture for protection.

Importantly, we’re not suggesting that space weather alone caused an increase in these behaviors or, certainly, that the Laschamps caused Neanderthals to go extinct, which is one misinterpretation of our research. But it could have been a contributing factor – an invisible but powerful force that influenced innovation and adaptability.

Cross-discipline collaboration

Collaborating across such a disciplinary gap was, at first, daunting. But it turned out to be deeply rewarding.

Archaeologists are used to reconstructing now-invisible phenomena like climate. We can’t measure past temperatures or precipitation directly, but they’ve left traces for us to interpret if we know where and how to look.

But even archaeologists who’ve spent years studying the effects of climate on past behaviors and technologies may not have considered the effects of the geomagnetic field and space weather. These effects, too, are invisible, powerful and best understood through indirect evidence and modeling. Archaeologists can treat space weather as a vital component of Earth’s environmental history and future forecasting.

Likewise, geophysicists, who typically work with large datasets, models and simulations, may not always engage with some of the stakes of space weather. Archaeology adds a human dimension to the science. It reminds us that the effects of space weather don’t stop at the ionosphere. They can ripple down into the lived experiences of people on the ground, influencing how they adapt, create and survive.

The Laschamps Excursion wasn’t a fluke or a one-off. Similar disruptions of Earth’s magnetic field have happened before and will happen again. Understanding how ancient humans responded can provide insight into how future events might affect our world – and perhaps even help us prepare.

Our unconventional collaboration has shown us how much we can learn, how our perspective changes, when we cross disciplinary boundaries. Space may be vast, but it connects us all. And sometimes, building a bridge between Earth and space starts with the smallest things, such as ochre, or a coat, or even sunscreen.

This article is republished from The Conversation, a nonprofit, independent news organization bringing you facts and trustworthy analysis to help you make sense of our complex world. It was written by: Raven Garvey, University of Michigan; Agnit Mukhopadhyay, University of Michigan, and Sanja Panovska, GFZ Helmholtz Centre for Geosciences

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Agnit Mukhopadhyay has received funding from NASA Science Mission Directorate and the University of Michigan Rackham Graduate School.

Raven Garvey and Sanja Panovska do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.