Biggest Black Holes Ever Found
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Biggest Black Holes Ever Found
No telescope has ever photographed the interior of a black hole, yet astronomers can tell you, with real error bars, that one sitting in the Cosmic Horseshoe galaxy weighs roughly 36 billion times as much as the Sun. That number comes from bent starlight, not a scale. This guide walks through the current record holders — TON 618, the Cosmic Horseshoe lens, Phoenix A*, M87*, and our own Sagittarius A* — and, more importantly, the four independent methods scientists use to weigh something that emits no light of its own.
What "biggest" actually measures
Black holes do not have a surface you can put a tape measure to, so "biggest" almost always means "most massive," not "largest in diameter." Mass and size are linked but not identical: a black hole's event horizon, the boundary past which nothing escapes, grows in direct proportion to mass through a formula called the Schwarzschild radius. Double the mass, and the horizon's radius doubles too.
That relationship is why a black hole with 40 billion solar masses has an event horizon roughly 40 billion times wider than one with a single solar mass, even though both are, in a sense, "just" points of infinite density at the center. The horizon is the part we can meaningfully compare across objects. It is also the boundary the Event Horizon Telescope imaged directly in 2019 for M87* and in 2022 for Sagittarius A*, producing the first actual pictures of a black hole's shadow rather than an artist's rendering (Event Horizon Telescope Collaboration, 2019).
Most black holes fall into three broad mass classes. Stellar-mass black holes, formed when massive stars collapse, typically run from about 5 to a few tens of solar masses; the largest confirmed stellar-mass black hole in the Milky Way, Gaia BH3, weighs about 33 solar masses and sits roughly 1,926 light-years away (ESO, 2024). Intermediate-mass black holes, a rarer and harder-to-confirm category, run from hundreds to tens of thousands of solar masses. Supermassive black holes, the kind that anchor galaxies, start around a million solar masses and, at the very top of the scale, cross into a category some astronomers now call "ultramassive": tens of billions of solar masses and up.
How you weigh something invisible
You cannot put a black hole on a scale, and you cannot see it directly, since by definition it emits no light. Instead, astronomers infer mass from how the black hole's gravity pushes, pulls, bends, or accelerates something nearby that is visible: stars, gas, or the light of a background galaxy. Four methods dominate the field, and each one is better suited to a different kind of target.
Stellar dynamics tracks the orbits of individual stars circling a black hole. This is the gold-standard method for our own galactic center: decades of infrared observations of stars orbiting Sagittarius A* let astronomers apply Kepler's laws directly, the same orbital mechanics that describe planets circling the Sun, to calculate a mass of about 4.3 million solar masses (Nobel Prize in Physics 2020 background, Reinhard Genzel and Andrea Ghez). It is precise, but it only works for black holes close enough that individual stars can be resolved, which in practice means the Milky Way and a handful of nearby galaxies.
Gas dynamics does the same job with orbiting clouds of ionized gas instead of stars, which lets astronomers probe closer to the black hole and reach targets much farther away than stellar dynamics allows. The tradeoff is that gas responds to forces beyond gravity alone, including radiation pressure and magnetic fields, so the math needs extra correction terms.
Reverberation mapping measures the time delay between flickers in a black hole's accretion disk (the hot, spiraling disk of infalling material) and the corresponding flicker in light emitted by gas clouds farther out. Because light travels at a fixed, known speed, that time lag converts directly into a distance, and combined with the gas velocity it yields a mass. This is one of the primary techniques for weighing active, light-emitting black holes called quasars, including TON 618 (Wikipedia summary of reverberation mapping methodology, sourced from peer-reviewed AGN literature).
Gravitational lensing is the newest and, for the very largest black holes, the most consequential method. General relativity predicts that mass bends light, so a black hole sitting directly between Earth and a distant background galaxy will warp that galaxy's light into arcs or a full ring, called an Einstein ring. By modeling exactly how much the light bent, astronomers back out the mass responsible. This is how the Cosmic Horseshoe black hole and an earlier record-setter in the galaxy Abell 1201 were measured, and it is one of the only techniques that works on black holes billions of light-years away, far too distant for stellar or gas orbits to be resolved individually (Astrobites summary of Abell 1201 lensing measurement, 2023).
A fifth, indirect shortcut called the M-sigma relation lets astronomers skip direct measurement entirely for galaxies where none of the above is practical. Research in the late 1990s and 2000s found a tight statistical correlation between a black hole's mass and the velocity dispersion (how fast stars randomly move) in the surrounding galactic bulge. Measure the bulge's stellar velocities, plug them into the relation, and you get an estimated mass, no direct orbit-tracking required. It is a population-level shortcut, not a precision instrument, and it tends to disagree with direct methods at the extreme high-mass end, which is part of why estimates for the biggest black holes bounce around from one paper to the next.
Why can't we just see a black hole directly?
A black hole's escape velocity exceeds the speed of light, so no photon that originates inside the event horizon can ever reach a telescope. What the Event Horizon Telescope imaged in 2019 and 2022 was not the black hole itself but its shadow: a dark silhouette cast against the glowing, superheated gas swirling just outside the horizon.
The current record holders
Mass estimates for the biggest black holes move by billions of solar masses between papers, sometimes because of new data and sometimes because of a change in method or model assumptions. The table below lists the objects most frequently cited as record holders, with the caveat that "TON 618" and "Cosmic Horseshoe" numbers in particular carry wide uncertainty ranges in the literature.
Table: Some of the most massive black holes identified as of 2026, by estimated mass
| Black hole | Estimated mass (solar masses) | Distance from Earth | Measurement method | Source |
|---|---|---|---|---|
| Cosmic Horseshoe (host galaxy J1004+4112) | ~36 billion | ~5 billion light-years | Gravitational lensing (Einstein ring) | Royal Astronomical Society, 2025 |
| TON 618 | ~40.7–66 billion (disputed) | ~10.4 billion light-years | Reverberation mapping / spectral line width | BBC Sky at Night Magazine |
| Abell 1201 BCG | ~32.7 billion | ~2.7 billion light-years | Gravitational lensing | Astrobites, 2023 |
| Phoenix A* (Phoenix Cluster) | Estimates range from ~5.8 billion to ~100 billion (unsettled) | ~5.7 billion light-years | Gas dynamics / X-ray modeling | NASA, Phoenix Cluster overview |
| M87* | ~5.4–6.5 billion | ~53.5 million light-years | Gas/stellar dynamics, confirmed by direct imaging | NASA Science, Messier 87 |
| Sagittarius A* (Milky Way) | ~4.3 million | ~26,000 light-years | Stellar dynamics (direct orbit tracking) | Nobel Prize in Physics 2020 |
| Gaia BH3 (largest confirmed stellar-mass black hole in the Milky Way) | ~33 | ~1,926 light-years | Astrometry (Gaia satellite) | ESO, 2024 |
Notice the spread on Phoenix A* and TON 618. Different research groups, using different methods and different assumptions about the geometry of surrounding gas, have produced numbers that vary by a factor of nearly twenty for the same object. That is not sloppy science; it reflects how hard it is to measure something you cannot directly image, sitting billions of light-years away, using light that left its source before complex life existed on Earth.
M87* deserves a special mention because it is the only entry on this list that has been measured two completely independent ways, once through gas and stellar dynamics and once through direct imaging of its shadow by the Event Horizon Telescope, and the two methods landed within the same general range. That agreement is part of why astronomers trust the underlying physics of black hole mass measurement even when individual numbers for more distant objects stay contested.
Why the record keeps changing
Space records shift for the same reason most scientific records shift: instruments get better, and models get revised. A record black hole announced in 2023 can lose its title in 2025 not because the object changed, but because someone pointed a sharper instrument at it, or because a team re-ran the same data through an improved model of how gas moves near an accretion disk.
The 2025 Cosmic Horseshoe measurement is a clean example. Gravitational lensing had already flagged Abell 1201's black hole as unusually massive in 2023, but the Cosmic Horseshoe's Einstein ring, an almost perfectly circular arc of light in this case, gave researchers an especially clean geometry to model, which tightened their confidence in the resulting 36-billion-solar-mass estimate (Royal Astronomical Society, 2025). TON 618's figure has moved the opposite direction: the widely quoted 66-billion figure came from an older analysis of the hydrogen-beta spectral line, and more recent reanalysis using updated calibration puts it closer to 40.7 billion, though the higher number remains more commonly cited in general reference sources simply because it circulated first (BBC Sky at Night Magazine).
This is a recurring pattern across astronomy, not just black holes. Exoplanet counts, the age of the universe, and the number of known galaxies have all been revised as new telescopes, from Hubble to JWST, extended what is observable. The honest way to report any "biggest" or "most" claim in astronomy is to name the measurement method and the date, because both actively shape the number.
Is there an upper limit to how big a black hole can get?
Theoretical astrophysicists think so, and the current crop of record-holders is bumping right up against it. The idea traces back to work on black hole self-regulation: as a black hole feeds on surrounding gas, the radiation released by the superheated infalling material pushes back on the gas supply itself, a balance point called the Eddington limit. Above a certain mass, roughly estimated in the tens of billions of solar masses, the feedback from the black hole's own feeding becomes strong enough to blow away or heat the surrounding gas reservoir faster than new material can fall in, effectively capping further growth (Space.com summary of ultramassive black hole growth-limit research).
That theoretical ceiling is one reason the Cosmic Horseshoe result generated more attention than a simple "new record" headline. At 36 billion solar masses, it sits close enough to the predicted maximum that researchers describe it as testing the limit rather than casually exceeding it. If future lensing surveys turn up something dramatically heavier, that would be a genuine surprise requiring revision of the self-regulation models. If instead every new ultramassive discovery clusters in the same 30-to-70-billion-solar-mass range no matter how researchers search, that consistency would itself be evidence the theoretical cap is real.
It helps to have an analogy here. Think of a black hole's growth like a bonfire being fed sticks in a wind: past a certain size, the fire's own heat and turbulence start throwing sticks away from the flame faster than a person can add them, capping how large the fire can get regardless of the wood supply. A black hole's radiation does something similar to its gas supply once the black hole gets big enough.
What people get wrong about "the biggest black hole"
The most common misconception is treating black hole mass and black hole danger as the same thing. A 36-billion-solar-mass black hole sounds terrifying, but its gravitational influence only dominates within its own galaxy, and even there, only close to the center. The Cosmic Horseshoe's black hole is roughly 5 billion light-years away; nothing about its mass changes anything measurable on Earth. Distance, not mass alone, determines whether a black hole matters to you.
A second mix-up is conflating a black hole's event horizon size with its physical bulk in the everyday sense of "big." Ultramassive black holes have event horizons that would swallow our entire solar system many times over, roughly 30 to 40 times the width of the solar system in TON 618's case according to several public estimates, yet the object at the center remains, in general relativity's description, a point of effectively zero volume. "Big" here describes the reach of extreme gravity, not a solid object with a surface area you could paint.
A third error, common in headlines rather than in the underlying papers, is presenting a single mass number as settled fact. As the table above shows, TON 618 and Phoenix A* both carry mass ranges that differ by a factor of two to twenty depending on method and paper. A precise-sounding number without a citation, a date, or a method attached should be treated as a rough midpoint at best, not a verified constant.
Finally, people sometimes assume that because a supermassive black hole sits at a galaxy's center, it must have "eaten" most of the galaxy's mass to get there. In reality, even a 36-billion-solar-mass black hole is a small fraction of its host galaxy's total mass once stars, gas, and dark matter are counted. The M-sigma relation exists precisely because black hole mass correlates with galaxy properties without the black hole dominating the galaxy's total mass budget.
Why this matters beyond the record chart
Ultramassive black holes are not just a curiosity for record lists; they are a stress test for galaxy formation theory. Models of how galaxies and their central black holes grow together predict that black hole mass should scale with the mass of the surrounding galactic bulge, which is exactly what the M-sigma relation captures at more modest scales. When a black hole's measured mass sits close to the theoretical growth ceiling, as the Cosmic Horseshoe's does, it gives theorists a real data point to check their self-regulation models against, rather than a purely mathematical prediction.
There is also a direct link to the earliest black holes in the universe. James Webb Space Telescope observations have found supermassive black holes in galaxies that existed when the universe was less than a billion years old, growing far faster than standard models predicted was possible. Understanding how large black holes can get, and how quickly, feeds directly into that separate but related puzzle of early-universe black hole growth.
The takeaway
The biggest confirmed black holes, currently topped by the roughly 36-billion-solar-mass object in the Cosmic Horseshoe galaxy, are measured indirectly through bent light, orbiting gas, or stellar motion, never by direct observation of the black hole itself. Every number in this field comes with a method, a date, and an uncertainty range attached, and all three of those change as instruments improve. The fact that several independent ultramassive discoveries now cluster near the same theoretical growth ceiling is arguably more scientifically interesting than which single object currently holds the title.
Frequently Asked Questions
Q: What is the biggest black hole ever found? A: As of 2026, the black hole in the Cosmic Horseshoe galaxy, estimated at about 36 billion solar masses and measured through gravitational lensing, is among the most massive confirmed. TON 618 is also frequently cited, with mass estimates ranging from roughly 40.7 to 66 billion solar masses depending on the analysis method (Royal Astronomical Society, 2025; BBC Sky at Night Magazine).
Q: How do scientists measure the mass of a black hole they cannot see? A: They track something the black hole's gravity affects: the orbital speed of nearby stars (stellar dynamics), the motion of surrounding gas (gas dynamics), time delays in flickering light (reverberation mapping), or the bending of background light (gravitational lensing). Each method suits different distances and target types.
Q: Is there a limit to how massive a black hole can get? A: Theoretical models suggest an upper limit somewhere in the tens of billions of solar masses, driven by radiation feedback from the black hole's own feeding process pushing away its gas supply, a mechanism related to the Eddington limit. Several ultramassive discoveries now cluster near this predicted ceiling (Space.com).
Q: How much bigger is the biggest black hole than the one in our Milky Way? A: Sagittarius A*, the Milky Way's central black hole, is about 4.3 million solar masses. TON 618 is roughly 15,300 times more massive than that, according to comparative estimates cited by BBC Sky at Night Magazine.
Q: Why do mass estimates for the same black hole vary between sources? A: Different research teams use different methods, instruments, and model assumptions about gas geometry or spectral line calibration. Phoenix A* and TON 618 both have published mass ranges that differ by a factor of two or more, which is why any single cited number should include its method and publication date.
Q: Has anyone actually photographed a black hole? A: Yes, but not the black hole itself. The Event Horizon Telescope produced the first image of a black hole's shadow, cast against glowing surrounding gas, for M87* in 2019 and for Sagittarius A* in 2022. No photon from inside the event horizon can ever reach a telescope, so what's imaged is the silhouette, not the object.
Q: What is the largest black hole in the Milky Way? A: For stellar-mass black holes, Gaia BH3 holds the record at about 33 solar masses, discovered using the Gaia satellite's astrometric data in 2024. The Milky Way's central supermassive black hole, Sagittarius A*, is separately measured at about 4.3 million solar masses.
Q: What's the difference between a supermassive black hole and an "ultramassive" one? A: Supermassive black holes generally range from about 1 million to several billion solar masses and anchor most large galaxies. Some astronomers use "ultramassive" informally for the rare objects above roughly 10 billion solar masses, though the term is not yet a formally standardized category.
Q: Does a bigger black hole mean it's more dangerous to Earth? A: No. Gravitational influence depends on distance as much as mass. The Cosmic Horseshoe's black hole is roughly 5 billion light-years away and has no measurable effect on anything in our solar system. A much smaller black hole nearby would matter far more than a giant one billions of light-years away.
Q: Why does black hole mass matter for understanding galaxies? A: Black hole mass correlates tightly with properties of its host galaxy's bulge, a pattern called the M-sigma relation. Because ultramassive black holes push against a predicted growth ceiling, they act as a real-world check on models of how galaxies and their central black holes form and grow together.
Read next:
- Black Holes Explained: How They Work
- How Do We Actually Find Exoplanets?
- What Would Happen If You Fell Into a Black Hole?
Sources
- Royal Astronomical Society: "Most massive black hole ever discovered" is detected (2025)
- Guinness World Records: Heaviest black hole
- BBC Sky at Night Magazine: TON 618
- Astrobites: Gravitational lensing unveils an ultramassive black hole in Abell 1201 (2023)
- NASA: Animation sizes up the universe's biggest black holes
- NASA Science: Messier 87
- Event Horizon Telescope Collaboration: First image of a black hole (2019)
- Nobel Prize in Physics 2020 press release: Genzel and Ghez, Sagittarius A*
- ESO: Most massive stellar black hole in our galaxy found, Gaia BH3 (2024)
- Space.com: How big can "ultramassive" black holes get?
- Wikipedia (sourced from peer-reviewed AGN literature): Reverberation mapping
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