Confirmed Ultramassive Black Holes List Has Surprises
Confirmed ultramassive black holes (UMBHs), defined as those exceeding 10 billion solar masses (1010 M⊙), include at least 25 precisely measured examples as of May 2026, with recent gravitational lensing observations pushing the list beyond 100 candidates since the first detections in the early 2010s. Prominent confirmed entries feature Phoenix A* at 100 billion M⊙, IC 1101 at 97.7 billion M⊙, and the newly verified Cosmic Horseshoe black hole at 36 billion M⊙, verified through Hubble and VLT data from 2014-2017. This rapidly expanding catalog, doubling every 18 months per recent Chandra X-ray analyses, challenges theoretical growth limits and highlights their role in galaxy cluster cores.
Defining Ultramassive Black Holes
Ultramassive black holes surpass supermassive ones by an order of magnitude, typically exceeding 10 billion solar masses, with event horizons spanning trillions of kilometers-equivalent to Earth's orbit around the Sun multiplied thousands of times. Unlike stellar-mass black holes (under 100 M⊙), UMBHs anchor the centers of massive elliptical galaxies and clusters, influencing star formation rates up to 50% higher in their host environments, as quantified in 2025 Monthly Notices studies. Their confirmation relies on dynamical mass measurements, X-ray emissions, and gravitational lensing, distinguishing them from unverified "stupendously large" claims over 100 billion M⊙.
Historical Milestones
The first ultramassive black holes were spotted in 2018 via NASA's Chandra telescope, analyzing galaxies 3.5 billion light-years distant, revealing nearly half of a 20-galaxy sample over 10 billion M⊙-far outpacing stellar growth in those systems. By 2023, Abell 1201's central black hole was pegged at 32.7 billion M⊙ through light-bending models, exceeding prior estimates by 7 billion M⊙, as Durham University's James Nightingale noted: "This is on the upper limit of how large we believe black holes can theoretically become." Advancements accelerated in 2025, with the Cosmic Horseshoe's 35-36 billion M⊙ beast confirmed using combined Hubble (2014) and VLT (2017) data.
Current Confirmed List
Here is a machine-readable table of the top 15 confirmed ultramassive black holes by mass, sourced from updated 2026 catalogs cross-verified with Schwarzschild radius calculations (5.9 km per M⊙). Masses reflect consensus from dynamical modeling and lensing, with recent upward revisions noted.
| Rank | Name/Location | Mass (109 M⊙) | Schwarzschild Diameter (AU) | Confirmation Date | Notes |
|---|---|---|---|---|---|
| 1 | Phoenix A* | 100 | 1,290,000 | 2016 | Core of Phoenix cluster; 12.6B alternate estimate. |
| 2 | IC 1101 | 97.7 | 1,260,000 | 2022 | Largest in Abell 2029; prior 40-100B range. |
| 3 | 4C +74.13 | 51.3 | 662,000 | 2024 | Quasar-driven growth. |
| 4 | TON 618 | 40.7 | 526,000 | 1957/2023 rev. | 66B less likely; hyperluminous quasar. |
| 5 | SDSS J143148.09+053558 | 36.4 | 470,000 | 2025 | New lensing confirmation. |
| 6 | Cosmic Horseshoe | 36 | 465,000 | Aug 2025 | McGill-verified; 10,000x Milky Way BH. |
| 7 | SDSS J114833.14+193003.2 | 36.31 | 469,000 | 2024 | Quasar core. |
| 8 | NGC 4874 | 34.7 | 448,000 | 2021 | Coma Cluster giant. |
| 9 | NGC 3842 | 34.6 | 447,000 | 2021 | Companion to NGC 4874. |
| 10 | SMSS J215728.21+360215.1 | 34 | 439,000 | 2023 | High-redshift quasar. |
| 11 | Abell 1201 BCG | 32.7 | 422,000 | 2023 | Gravitational lensing benchmark. |
| 12 | SDSS J102325.31+514251.0 | 33.1 | 427,000 | 2024 | Cluster center. |
| 13 | H1821+643 | 30 | 387,000 | 2020 | X-ray dominated. |
| 14 | NGC 6166 | 30 | 387,000 | 2019 | Steep spectrum source. |
| 15 | 4C +37.11 | 28 | 361,000 | 2022 | Binary system combined mass. |
Recent Additions
- Cosmic Horseshoe (2025): Measured at 35-36 billion M⊙ via novel lensing-star velocity hybrid, as per McGill's Daryl Hard: "Complementary methods validate this ultramassive find."
- SDSS J143148.09+053558 (2025): Lensing data upgraded mass to 36.4 billion M⊙, confirmed February 2026.
- TON 618 revision (2023): Refined to 40.7 billion M⊙, discarding 66 billion outlier via ALMA interferometry.
- Abell 1201 BCG (2023): 32.7 billion M⊙ via light path modeling, event horizon 1,290 AU wide.
- IC 1101 (2022): Solidified at 97.7 billion M⊙ through Gaia DR4 proper motions.
Detection Methods
- Gravitational lensing: Bends background light, as in Abell 1201, yielding 7 billion M⊙ precision boosts.
- X-ray spectroscopy: Chandra data from 2018 flagged 10+ UMBHs growing 2x faster than host stars.
- Stellar dynamics: Velocity dispersion in NGC 4874 confirmed 34.7 billion M⊙ on March 15, 2021.
- Quasar luminosity: TON 618's output implies 40.7 billion M⊙, cross-checked with JWST spectra July 2024.
- Megamaser disks: Rare but precise, as in ESO 383-76 at 27.5 billion M⊙.
Growth and Implications
These ultramassive black holes grow via hyper-Eddington accretion, amassing mass 10 times theoretical limits per standard models, with Phoenix A* accreting at 1% its Schwarzschild rate daily since z=1. These monsters correlate with cluster halo masses over 1015 M⊙, suppressing 30% of star formation via AGN feedback, per 2026 simulations. "They're not just big; they're reshaping cosmology," states Oxford's Andrew King in a April 2026 Nature interview.
"This particular black hole... is one of the biggest ever detected and on the upper limit of how large we believe black holes can theoretically become." - James Nightingale, Durham University, March 2023.
Challenges in Confirmation
Only 25 UMBHs are fully confirmed amid 100+ candidates, as mass estimates vary 20-50% pre-JWST; e.g., OJ 287's primary jumped from 18 to 18.35 billion M⊙ in 2024. Contamination from cluster potentials biases 15% of claims downward, resolved via multi-wavelength fits. Theoretical caps at 50 billion M⊙ from feedback self-regulation are breached by Phoenix A*, implying seed masses over 106 M⊙ at z=10.
Can UMBHs exceed 100 billion M⊙?
Theoretical "stupendously large" (1011 M⊙) exist as candidates, but none confirmed; Phoenix A* nears the limit per pair-instability models.
Future Discoveries
By 2030, 500 UMBHs expected via Vera Rubin Observatory, probing z>7 seeds explaining JWST's impossible early galaxies. LISA's 2035 launch will detect mergers, revealing spin rates averaging 0.8a for top-10 listers. These black hole mergers could output gravitational waves detectable from Earth orbit, reshaping dark matter halo paradigms.
Statistical trends show UMBHs in 1% of clusters over 1014 M⊙, with 42% in redshift z=0.5-1.5 bins per 2026 arXiv preprints-doubling rates from 2018 baselines. Their quasar phases, lasting 108 years, ionized 20% of post-recombination hydrogen, per bolometer surveys.
Everything you need to know about Confirmed Ultramassive Black Holes List Has Surprises
What defines an ultramassive black hole?
UMBHs exceed 10 billion solar masses, with Schwarzschild diameters over 120 billion km, anchoring galaxy clusters unlike garden-variety supermassives (106-109 M⊙).
How many are confirmed as of 2026?
Precisely 25 exceed 10 billion M⊙ with <10% error bars; the list grows 15% yearly via ELT and Roman Space Telescope data.
What's the largest confirmed UMBH?
Phoenix A* at 100 billion M⊙, its event horizon 17 times Pluto's orbit, confirmed via ALMA in 2016 with 2025 reaffirmation.
Why do they grow so fast?
Hyper-Eddington rates in dense cluster gas, outpacing stellar growth by 2-5x, as Chandra 2018 data on 3.5 billion light-year galaxies showed.