What is the biggest black hole? Why there is no confirmed record

No black hole holds a confirmed “biggest” title: the most massive black holes weighed by direct methods contain roughly 30–40 billion times the Sun’s mass (about 6–8 × 10⁴⁰ kg), while larger figures—up to 100 billion Suns or more for Phoenix A—come from indirect, model-dependent estimates. For comparison, the black hole at the centre of our Milky Way, Sagittarius A*, holds about 4.3 million solar masses.

The leading candidates are TON 618 (about 41–66 billion solar masses, inferred from quasar light), Holm 15A (40 ± 8 billion, from stellar motions), the black hole in the Cosmic Horseshoe lens galaxy (about 36 billion, from lensing and stellar motions) and the Abell 1201 cluster galaxy (about 33 billion, from lensing). Which one is truly heaviest depends as much on measurement method as on the headline number.

Key facts about the biggest black holes

• Largest directly measured masses: about 3–4 × 10¹⁰ solar masses (Holm 15A, the Cosmic Horseshoe, Abell 1201).
• Largest published quasar estimate: TON 618, at about 6.6 × 10¹⁰ solar masses in a 2004 analysis and about 4.1 × 10¹⁰ in a later recalculation.
• Largest popular figure: about 10¹¹ solar masses for Phoenix A, which comes from a theoretical growth scenario, not a measurement.
• Proposed ceiling: one theoretical study puts the limit for black holes that grow by shining gas accretion near 5 × 10¹⁰ solar masses, rising to about 2.7 × 10¹¹ in extreme cases.
• Event-horizon scale: a non-spinning 40-billion-solar-mass black hole would be about 1,600 astronomical units (AU) across—roughly 26 times the diameter of Neptune’s orbit.

Which black holes are the biggest? Ranked by published mass

The table lists each object’s highest commonly cited estimate first, but the confidence column matters more. A large number from an indirect method is weaker evidence than a slightly smaller number from a direct method.

Source note: masses and redshifts come from the papers listed under Sources. Light-travel times were calculated by SciQuest for a flat universe with Planck 2018 parameters (H₀ = 67.4 km/s/Mpc, Ωm = 0.315); the Chandra X-ray Center gives about 5.7 billion light-years for the Phoenix cluster. One solar mass is about 1.99 × 10³⁰ kg.

Why is there no confirmed biggest black hole?

Astronomers cannot put a black hole on a scale. They infer its mass from how its gravity affects something they can observe, and the reliability of that inference differs sharply by method.

• Stellar or gas dynamics model how stars or gas move near the centre of a galaxy. This is how Holm 15A was weighed. It works only for galaxies near enough for telescopes to resolve those motions.
• Gravitational lensing measures how the galaxy’s total mass bends light from a more distant galaxy. A compact extra mass at the centre changes the lensed image in a measurable way. This weighed Abell 1201 and, combined with stellar motions, the Cosmic Horseshoe.
• Reverberation mapping times the delay between changes in a quasar’s brightness and the response of surrounding gas. It provides the calibration for the faster single-epoch virial method, which estimates mass from one spectrum: line width for gas speed and brightness for distance from the black hole. TON 618’s numbers come from this route.
• Accretion-disc fitting compares a quasar’s spectrum with disc models; it was used for S5 0014+81.
• Scaling relations and energy arguments infer a mass from host-galaxy properties or from the energy needed to heat cluster gas. These are useful for populations but weakest for extreme individual objects. The largest Phoenix A figures belong here.

Single-epoch estimates have absolute uncertainties of typically about a factor of four, according to the calibration study by Vestergaard and Peterson. TON 618 also lies far above the brightness range of the reverberation-mapped galaxies used to calibrate the method, a limitation its 2004 analysis acknowledged.

Why do direct measurements top out around tens of billions of Suns?

The three strongest direct measurements in this range—Holm 15A, the Cosmic Horseshoe and Abell 1201—all land between about 3 and 4 × 10¹⁰ solar masses. Part of the reason is practical. Dynamical methods need sharp views of a galaxy’s core, which limits them to relatively nearby systems. Lensing needs a rare chance alignment with a background galaxy. Very few of the most massive galaxies satisfy either condition.

There may also be a physical reason. In a 2016 study, astrophysicist Andrew King calculated a maximum mass for black holes that grow by luminous gas accretion: about 5 × 10¹⁰ solar masses for typical parameters, or about 2.7 × 10¹¹ in extreme cases such as maximal prograde spin. That is the source of the “50–270 billion” upper-limit range often quoted. King noted that the limit rests on a reasonable but currently untestable hypothesis about how accretion discs form, and that black holes could still exceed it by merging—though they could not then shine as quasars or other active nuclei.

Black holes above 10¹¹ solar masses have been called “stupendously large black holes.” Carr, Kühnel and Visinelli examined how such objects could be constrained, and suggested some might even have been seeded by primordial black holes. That work is theoretical; no black hole has been measured at that mass.

How big is the event horizon of the biggest black holes?

For a non-spinning black hole, the event-horizon radius is the Schwarzschild radius, r = 2GM/c². That works out to about 2.95 km for every solar mass, so the radius grows in direct proportion to mass.

Worked example for 4.0 × 10¹⁰ solar masses: 2.95 km × 4.0 × 10¹⁰ ≈ 1.18 × 10¹¹ km. Dividing by 149.6 million km per AU gives a radius of about 790 AU and a diameter of about 1,580 AU.

Calculated by SciQuest from GM☉ = 1.327 × 10¹¹ km³/s² (NASA Sun Fact Sheet), c = 299,792.458 km/s and 1 AU = 149,597,870.7 km. Spinning black holes have smaller horizons than this non-spinning approximation.

Neptune orbits the Sun at about 30 AU, so the diameter of its orbit is about 60 AU. A 40-billion-solar-mass horizon would span about 26 Neptune orbits laid end to end. Even so, 1,580 AU is only about 0.025 light-years—minute on the scale of the galaxy that hosts it.

Is TON 618 bigger than Phoenix A?

Nobody can say yet. If the 2012 Chandra figure of about 20 billion solar masses is close, TON 618 is the larger of the two. If Phoenix A is near the 100-billion upper scenario, it is larger. Neither number comes from a direct measurement, so ranking them is not meaningful. Our side-by-side comparison of Phoenix A, TON 618 and Holmberg 15A sets out the evidence for each, and the TON 618 size explainer shows how its event horizon is calculated.

What happened to older “top 5 biggest black hole” lists?

Older lists, including a previous SciQuest page, often ranked Phoenix A first at exactly 100 billion Suns, followed by TON 618 at 66 billion, Holm 15A, IC 1101 and S5 0014+81 at about 40 billion each. Several of those entries have since changed or need context:

• Phoenix A: the 100-billion figure comes from a 2016 modelling study that said the black hole “might” exceed 10¹¹ solar masses. A 2025 JWST study instead argued for a mass nearer 10¹⁰, while noting it is only weakly constrained. Our Phoenix A black hole profile traces each estimate.
• S5 0014+81: its 2009 estimate of about 4 × 10¹⁰ solar masses was revised in 2016 to about 7.5 × 10⁹ after infrared data from NASA’s WISE mission were added and older optical data were set aside.
• IC 1101: its black hole has not been weighed directly. A 2017 study of the galaxy’s unusually large core suggested about 4–10 × 10¹⁰ solar masses, an interpretation based on how merging black holes scour out stars.
• Abell 1201 and the Cosmic Horseshoe: both were added after 2022 because lensing gave direct detections. SciQuest covered the Abell 1201 lensing result when it was announced.

Is the biggest black hole also the biggest object in space?

No. A black hole’s mass can exceed that of a large star by a factor of billions, but its horizon is still far smaller than a galaxy. Size comparisons also depend on what is being measured. Our explainer on Stephenson 2-18 vs Phoenix A compares a red supergiant star’s physical radius with a black hole’s event-horizon radius.

What scientists don’t know yet

• Whether any black hole exceeds about 10¹¹ solar masses. None has been measured there.
• How accurate single-epoch masses are for the most luminous quasars, which lie beyond the range used to calibrate the method.
• Phoenix A’s actual mass. A dynamical or lensing measurement would settle whether it is undermassive or among the largest known.
• Whether King’s proposed ceiling holds. It depends on accretion-disc physics that cannot yet be tested directly.

Related reading

• Phoenix A vs TON 618 vs Holmberg 15A: which black hole is heaviest?
• What is at the centre of the Milky Way? Sagittarius A* explained
• What is the closest supermassive black hole to Earth?

Update note: This article was substantially revised on October 12, 2026, to remove the unsupported claim that Phoenix A is a confirmed 100-billion-solar-mass record holder and a primordial black hole, correct TON 618’s mass (previously given as 66 million) and the Phoenix A distance, age and size figures, add a sourced table with methods and uncertainties, note the downward revision of S5 0014+81, and incorporate the 2025 Cosmic Horseshoe measurement. It now also covers the content of our former “top 5 biggest black holes” page. It was drafted with AI assistance and checked against the sources listed below.

Sources

• Mehrgan et al., A 40 billion solar mass black hole in the extreme core of Holm 15A, The Astrophysical Journal 887, 195 (2019)
• Melo-Carneiro et al., Unveiling a 36 billion solar mass black hole at the centre of the Cosmic Horseshoe gravitational lens, Monthly Notices of the Royal Astronomical Society 541, 2853 (2025)
• Nightingale et al., Abell 1201: Detection of an ultramassive black hole in a strong gravitational lens, Monthly Notices of the Royal Astronomical Society (2023)
• Shemmer et al., Near-infrared spectroscopy of high-redshift active galactic nuclei. I., The Astrophysical Journal 614, 547 (2004)
• Ge et al., The blueshift of the C IV broad emission line in QSOs, The Astronomical Journal 157, 148 (2019); table data via CDS VizieR J/AJ/157/148
• Vestergaard and Peterson, Determining central black hole masses in distant active galaxies and quasars. II., The Astrophysical Journal 641, 689 (2006)
• Brockamp et al., Unveiling Gargantua: a new search strategy for the most massive central cluster black holes, Astronomy & Astrophysics 585, A153 (2016)
• Reefe et al., Cold gas and star formation in the Phoenix cluster with JWST, accepted by The Astrophysical Journal (2025)
• NASA Chandra X-ray Center, Phoenix Cluster Sets Record Pace at Forming Stars (August 15, 2012)
• Ghisellini et al., The blazar S5 0014+813: a real or apparent monster?, MNRAS Letters 399, L24 (2009)
• Sbarrato et al., Extremes of the jet–accretion power relation of blazars, as explored by NuSTAR, Monthly Notices of the Royal Astronomical Society (2016)
• Dullo, Graham and Knapen, A remarkably large depleted core in the Abell 2029 BCG IC 1101, Monthly Notices of the Royal Astronomical Society 471, 2321 (2017)
• Event Horizon Telescope Collaboration, First M87 Event Horizon Telescope Results. VI. The shadow and mass of the central black hole, The Astrophysical Journal Letters 875, L6 (2019)
• GRAVITY Collaboration, The mass distribution in the Galactic Centre from interferometric astrometry of multiple stellar orbits, Astronomy & Astrophysics (2022)
• King, How big can a black hole grow?, MNRAS Letters 456, L109 (2016)
• Carr, Kühnel and Visinelli, Constraints on stupendously large black holes, Monthly Notices of the Royal Astronomical Society 501, 2029 (2021)
• Planck Collaboration, Planck 2018 results. VI. Cosmological parameters, Astronomy & Astrophysics 641, A6 (2020)
• NASA NSSDCA, Sun Fact Sheet and Planetary Fact Sheet