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.
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.
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By WrongOnInternet 2025-07-1421:278 reply > 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.
Does this mean that 15 solar masses were converted into energy? Because that's a LOT of energy.
By aaronharnly 2025-07-150:277 reply Let’s see — the Tsar Bomba nuclear weapon released the equivalent of converting about 2.3 kg of matter into energy (1).
One solar mass is about 2 x 10^30 kg, so round numbers this event released the same as 10^31 Tsar Bombas, which is … a lot of energy? That number is too big to be a good intuition pump.
Let’s try again: over the course of its entire lifetime of about 10 billion years, the sun will release about 0.034% of its mass as energy (2). So one solar mass of energy is about 3000 solar-lifetime-outputs.
So this event has released about as much energy as 45,000 suns over their entire lifetime. I’m not sure how much of the energy was released in the final few seconds of merger, but probably most of it? So… that’s a lot of energy.
By randomtoast 2025-07-156:181 reply > this event released the same as 10^31 Tsar Bombas, which is … a lot of energy? That number is too big to be a good intuition pump
Let me try:
To match this power with sequentially detonated bombs, one would need to set off about 10^13 Tsar Bombas (or one hydrogen bomb scaled up to 5% the mass of the Moon) every second since the Big Bang to match it. With that amount of energy, you could essentially destroy earth every second since the Big Bang.
By HenryBemis 2025-07-156:461 reply [flagged]
By randomtoast 2025-07-1511:521 reply I don’t want to dismiss your memory of the anecdote, but it doesn’t hold up under fact-checking. https://www.snopes.com/fact-check/bono-of-contention/
By HenryBemis 2025-07-1516:08 I don't care about the anecdote and its origin (but I did read this and thank you for setting the record straight). I don't care about Bono either :) He's a singer in a band that once made great music, and got lots of money, and does some good things about it. It's the parallelism of the statements 'stop clapping' x 'stop setting off bombs' that cracked me up.
Yeah, it's alot alot :-). Over on Mastodon I asked Phil Plait (@badastro) if the "missing mass" in the universe might be a result of black holes converging[1]. He wrote up this event in his newsletter[2] and points out that when they merge, they emit more energy in that instant than every single start in the universe in the same instant. So kind of like an instant of double energy. Hard to fathom how much energy that is with my meager mammalian brain.
[1] https://mastodon.social/@badastro/114852139083587160
[2] https://badastronomy.beehiiv.com/p/the-biggest-black-hole-me...
I can't even understand how supernovae emit like "more energy than than the sun over it's entire lifetime"
Just... how? I get what happens with fusion but the numbers are so mind boggling. And it makes what seems like a terrifying ball of fire appear as a space heater in comparison. It's nuts. The GW thing you mention is near incomprehensible to me.
By dredmorbius 2025-07-1518:56 One of the rather curious facts about the Sun is that its net energy emissions, on a unit-mass basis, are roughly the same as a mammalian metabolism.
That is, your body is converting mass to energy (the only way the conversion is possible) through chemical processes (ATP-mediated molecular breakdown in the Krebs cycle) at roughly the same rate that the Sun is converting mass to energy through fusion of hydrogen to helium (modulo some pathway hand-waving).
You'll need far more input chemical fuel (carbohydrates and fats, mostly) than the Sun needs of input hydrogen fuel. But the net energy release rate is roughly equivalent.
The biggest difference between you and the Sun is that it (presumably) weighs somewhat more than you do. So that per-unit-mass conversion is multiplied by a much greater mass.
By jerf 2025-07-1516:53 At this scale it can help to think in terms of mass rather than energy. The most energy the sun could ever emit over its lifetime is if it was completely converted into energy. However, this merger emitted 15 times the mass of the sun as energy. I don't have all the numbers on tap for supernovas but given that the sun won't convert all its mass to energy, it's not hard for a supernova to convert more mass in its explosion into energy than the sun ever will.
By dtgriscom 2025-07-1521:51 You mean "every single star in the universe", right?
By twothreeone 2025-07-1519:22 Observable universe. Dark matter does not emit light.
By vjvjvjvjghv 2025-07-150:292 reply I have read somewhere that an experiencing a supernova at sun distance would be the same as holding a hydrogen bomb to your eyeball. The energy released in these events is basically unimaginable.
By aaronharnly 2025-07-151:382 reply Probably here:
And it’s even more astonishing — the supernova at 1 AU would be the same as a billion hydrogen bombs at your eyeball.
By bravesoul2 2025-07-1510:284 reply But you are safe at a parsec. Showing how also incredibly big space is. Space's bigness makes it hard to blow up a galaxy. Big bang excepted.
By ordu 2025-07-1512:34 It depends on the kind of supernova. Type Ia[1] is really insane. 10^44 J is a thing, that I think can blind you, even you've chosen a spot for your picnic to watch a Big Boom at distance of 1 parsec. A white dwarf made mostly of carbon burns all the carbon into oxygen in matter of seconds, and then it burns some of oxygen that was a result of burning carbon. It would like to continue brewing more and more heavy elements, but can't, because it becomes so hot, that gravity is no longer enough to keep the matter from flying away.
By thechao 2025-07-1512:29 All the stars in the universe, burning as brightly as they are, are the tiniest fraction of additional energy compared to the 2.73°K background temperature of space. The Big Bang was very warm.
By bravesoul2 2025-07-161:48 Yes the same reasons your jet wash can't water your entire garden at once.
By mr_toad 2025-07-1512:27 For certain values of safe. It’s close enough to strip the ozone layer, significantly increase the risk of cancer, alter the climate, and possibly cause extinctions.
By mytailorisrich 2025-07-158:451 reply Another way to look at it is that a hydrogen bomb is very small at planetary scale and so microscopically small at any astronomical scale.
By aaronharnly 2025-07-1518:43 I appreciate this point – it would take quite a few Tsar Bombas to approach the binding energy of a planet.
But, is it a small or large hydrogen bomb? And, what distance from your eyeball?
By dredmorbius 2025-07-1519:08 At these scales, several orders of magnitude literally makes no difference.
Hydrogen bomb yields range from roughly 0.1 MT to 100 MT (the full design yield of the Tsar Bomba), or four orders of magnitude. They can be considered equivalent for the purposes of this comparison. The principle warhead of the US ICBM force, the W87 warhead, has yield of ~0.3 to 0.475 MT.
Even at a distance of several tens of metres from your eye, destructive effects would remain significant.
By vjvjvjvjghv 2025-07-158:40 I’ll run some tests and let you know
Assuming your 0.034% figure is correct, then one solar mass is equivalent to 2941 lifetimes of a sun's output, not 30. So 15 solar masses would be more like 44115 solar-lifetimes.
By aaronharnly 2025-07-151:33 Derp yes, pesky off-by-100 errors :) Fixed, thanks.
Also to put in perspective, most of the mass isn't converted to energy in either nuclear or hydrogen bombs, it's just the bond energy. Pure energy for a given quantity of matter is released only in case of annihilation-like event(merging with anti matter). So even fusion releases max 0.7% energy of the mass
I'm not sure what happens in black hole merger.. is it an annihilation like event or is just fusion...
By simonh 2025-07-1514:17 The black holes orbit each other, and get closer and closer. This emits gravity waves, and when they merge a large proportion of their combined mass gets emitted as gravity waves. These are what LIGO is detecting.
By arbitrandomuser 2025-07-1514:591 reply The bond energy is also mass . Energy is mass , If you had a nuclear reactor surrounded by gas and this setup ran a turbine which compressed a humungous spring and this whole setup was completely sealed and sits on a gigantic weighing scale. You run the nuclear reactor, the spring compresses gaining potential energy, waste heat goes into the gas molecules as kinetic energy. As the reactor progresses converting "mass to energy" does the weighing scale become lighter ?
By deepsun 2025-07-1520:37 Well, weighing scale doesn't measure mass, it measures weight. It's just scales' UI converts it to kg/lb for usability, instead of showing N it actually measures (weight is a force, and force is measured in newtons).
By steve_adams_86 2025-07-1519:461 reply It's humbling to consider what an incredibly low-energy state we humans live in. The universe is capable of such immense energetic outputs. We're humming along at energy levels approaching zero compared to most bodies floating around in space. Crazy.
If you consider orders of magnitude from the Planck scale all the way up to the observable universe, we are actually somewhere in the middle
By steve_adams_86 2025-07-166:25 I hadn't considered that! That makes me wonder... Is that likely to be true for most forms of life? I wonder if there's some physical constraint that makes this likely. I suppose I won't know in my lifetime. It's also probably not so significant that we're close to the middle; maybe it's just my ape brain finding significance in arbitrary figures.
If I were to guess before, I think I would have estimated humanity was in the lower 10%. I suppose I was mostly thinking in terms of the Kelvin scale.
It's fascinating to consider how staggering the scale goes in either direction, now. Absolutely bizarre.
Is it physically limiting for a theoretical civilization to harness and use such energy?
By Thiez 2025-07-1511:34 The energy is emitted as gravitational waves which is probably tricky to convert into usable energy and you probably can't attend more than one in your life unless you have faster-than-light travel. You're much better off visiting a supernova.
But in general it's better to have a steady and stable source of power, rather than one enormous burst of energy that you have to spend on something instantly.
Yes! And still, gravity is so weak that that immense amount of energy translates to just a relative contraction of less than 10^-20, or about a hair's width in the distance from the Earth to the Moon.
By ssl232 2025-07-157:09 This is because space is _stiff_. Recall Hooke’s law from high school physics. The k constant represents the stiffness of the object. A rubber band is about 50. A sky scraper, about a million. Space? About 10^46 if I recall correctly. So it takes a truly enormous amount of energy in the form of gravitational waves to be able to move space enough for it to be detectable on Earth. And the only objects that can do that are the most massive ones moving at close to the speed of light: black holes, neutron stars, supernovae (the latter would have to be very close for us to see gravitational waves from - close enough that we’d likely see it with the naked eye as well).
By UltraSane 2025-07-1423:39 At 10 times the Schwarzschild radius Space literally stretches and contracts by 10-100%
Do we know how far this event was from earth? Wouldn't that distance be the determiner of what the relative contraction observed on earth would be?
estimated distance of 2.2 Gpc per https://en.wikipedia.org/wiki/GW231123
By BurningFrog 2025-07-156:06 That's 7.2 billion light years. More than halfway to the most distant galaxy the Webb telescope has found.
So this event happened 7.2 billion years ago.
There is no mention of in which direction. Maybe the triangulation wasn't working at the time. You need three LIGOs for that.
By irjustin 2025-07-151:26 That's how fast the millennium falcon goes
By misja111 2025-07-1514:20 Sure but we are 7 billion lightyears away from the source of the waves. Imagine if we'd be a bit closer ..
By UltraSane 2025-07-1423:31 Yes. Black hole mergers are the highest energy events in the universe in terms of watts.
I was disappointed to learn that it would require billions of solar masses of energy from a black hole merger to be able to ride the gravitational wave starting at a distance of a few Schwarzschild radii. It seems like riding a plasma jet might be better.
(Just planning my next trip.)
By pixl97 2025-07-152:30 Much better off just chucking 90% of your mass into the blackhole to get a hella kick.
By tashmahalic 2025-07-154:042 reply Into what form of energy is that mass converted?
By BurningFrog 2025-07-155:562 reply Maybe all of it is gravitational waves?
I don't think much else would escape the black hole environment.
Need a bit of oomph to move the very fabric of this universe a bit. But energy conversation laws say its just then spread all over the place across time, just like ripples in pond, suspended into nothingness of its own little universe... or something
Tells me a bit darker thing in between the lines - the chance some advanced civilization (or us in far future if we actually survive) traveling FTL by bending space massively is next to zero, we would see (or detect soon) the evidence... unless they do it on planck-level of precision and self-contain all ripples. Nah, it really seems c is the ultimate barrier so far... depressing.
By mr_toad 2025-07-1512:33 > Need a bit of oomph to move the very fabric of this universe a bit.
It’s enough “oomph” that we can detect it more than half way across the universe.
By misja111 2025-07-156:53 Kinetic energy is another option
By csomar 2025-07-159:39 Pure energy.
Converted into energy and then escape the black hole, from which light can’t escape? That doesn’t seem to compute. And if it’s converted into gravity waves then we have an excellent obvious candidate for how most energy will escape a black hole. It won’t be waiting around for hawking radiation.
By dd_xplore 2025-07-1510:15 I think during the merger the event horizon must be changing rapidly, so I guess there's some(or a lot) of chance that matter can escape these merger events. The matter will already have high kinetic energy...
By veunes 2025-07-158:37 It's hard to wrap your head around, but that's more energy than all the stars in the observable universe combined put out during that instant
Can some of the mass escape as gas/mass flying out into space? Basically is energy the only way for mass to exit such an event?
By Thiez 2025-07-1512:00 No mass escapes. It is purely gravitational waves that are emitted. There is no sneak peek behind the event horizon curtain during a black-hole merger.
Man, that is some seriously interesting phenomena:
"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."
By veunes 2025-07-158:43 It's like nature handed us a stress test for general relativity
Does the spinning of a spherical object cause any gravitational waves?
By NL807 2025-07-1515:18 The rotating mass drags space time around it, called frame dragging, which is different from gravitational waves. Gravitational waves consists of oscillations, which is caused by change of mass, wobbling of spinning objects, or several masses orbiting around a barycentre.
A month ago, the proposed NSF budget would shut down one of the two LIGO observatories in the US, wrecking its ability to triangulate the location of events such as this black hole merger. A shutdown would also severely damage the noise margins and detection rate. Does anyone know if the shutdown is still planned? (I couldn't find any recent info.)
https://www.science.org/content/article/trump-s-proposed-cut...
I believe the proposed budget is being marked up tomorrow (July 15th, 12:00). Currently the NSF budget is set to be ~$7 billion, a 23% cut compared to FY2025. I'm not sure how this affects LIGO exactly.
https://appropriations.house.gov/sites/evo-subsites/republic...
By amarcheschi 2025-07-1422:211 reply I had read something less recent than what you posted, but in that is said about 40% of ligo funding would be cut https://www.science.org/content/article/trump-s-proposed-cut...
Then again, your file has less drastic reductions on nsf budget so who knows what would be the impact on ligo
By bee_rider 2025-07-152:42 I wonder why Bezos doesn’t just pick up the tab, he likes space, right?
By jedberg 2025-07-1423:32 > I believe the proposed budget is being marked up tomorrow (July 15th, 12:00)
Interesting that they break this news today. Props to them for playing the game.
By amarcheschi 2025-07-1422:09 I was last week at an event in Pisa at virgo ego (basically ligo's cousin). It was to celebrate the 10th anniversary of finding gravitational waves iirc. There were an actress reading from the book the director of the Italian program wrote accompanied by the sound of waves made with sax. I can't describe it with words but it was truly moving.
There were also moments dedicated to interviewing a science communicator and the director of the virgo center, and he was, let's say, quite angry at the thought of ligo losing funding. Rightfully so
By TMEHpodcast 2025-07-1423:21 Keep an eye on whether the final FY 2026 appropriations bill keeps LIGO at two sites. Until then, it’s a real risk, but salvageable.
By robin_reala 2025-07-158:122 reply Given that there’s a handful of gravitational-wave observatories running globally at this point, why does the closure of one LIGO wreck triangulation?
the collaboration to be able to triangulate is composed of LIGO, Virgo and now KAGRA. KAGRA is not yet fully ready for longer observation runs, so for now it's basically LIGO and Virgo - and if you take offline one of three, triangulation becomes nearly useless
By robin_reala 2025-07-1512:55 Looking at their Grafana dashboard, it looks like GEO600 and KAGRA are both observing? https://online.ligo.org/grafana/public-dashboards/1a0efabe65...
By BurningFrog 2025-07-156:121 reply So maybe that is why this discovery from 2023 gets published right now.
By gus_massa 2025-07-1512:38 I think all the previous events were announced with a big delay. They have a long pipeline of checks. The signals have too much noise and it's difficult not to cheat and find fake signals in the noise. IIRC they even have a team that adds secretly fake signals to ensure the pipeline is working and after it's detected the team disclose if it's real or fake, before publication.
