Most Massive Black Holes Ever Discovered
The 15 most massive black holes ever discovered, ranked by mass in billions of solar masses. Phoenix A leads at ~100 billion solar masses, followed by IC 1101 at ~97.7 billion and TON 618 at 40.7 billion.
Data
| # | Black Hole | Mass (Billion M☉) |
|---|---|---|
| 1 | Phoenix A | 100 |
| 2 | IC 1101 | 97.7 |
| 3 | 4C +74.13 | 51.3 |
| 4 | TON 618 | 40.7 |
| 5 | NGC 3842 | 34.6 |
| 6 | SMSS J2157 | 34 |
| 7 | Abell 1201 BCG | 32.7 |
| 8 | H1821+643 | 30 |
| 9 | NGC 6166 | 28.4 |
| 10 | 4C +37.11 | 28 |
| 11 | ESO 383-76 | 27.5 |
| 12 | Holmberg 15A | 21.6 |
| 13 | NGC 4889 | 21 |
| 14 | OJ 287 | 18.35 |
| 15 | NGC 1600 | 17 |
Note: The Most Massive Black Holes Ever Discovered
What Makes a Black Hole Massive
A black hole is a region of space where gravity is so intense that not even light can escape. Astronomers sort them by mass, from stellar-mass holes a few times the Sun's mass up to supermassive holes at the centers of galaxies. The objects on this list belong to an even rarer class sometimes called ultramassive black holes, each weighing tens of billions of solar masses or more.
The Heavyweight Champion
Phoenix A leads the list at roughly 100 billion solar masses, making it the most massive black hole ever discovered. It sits at the center of the Phoenix cluster, a galaxy cluster notable for producing enormous amounts of hot gas and new stars. For comparison, the black hole at the center of our own Milky Way, Sagittarius A*, weighs only around 4 million solar masses, meaning Phoenix A outweighs it by a factor of roughly 25,000.
The Billion-Solar-Mass Club
- IC 1101 (2nd): about 97.7 billion solar masses.
- 4C +74.13 (3rd): about 51.3 billion solar masses.
- TON 618 (4th): about 40.7 billion solar masses.
- NGC 3842 (5th): about 34.6 billion solar masses.
- SMSS J2157 (6th): about 34 billion solar masses.
- Abell 1201 BCG (7th): about 32.7 billion solar masses.
- H1821+643 (8th): about 30 billion solar masses.
How Astronomers Measure Them
No telescope can see a black hole directly. Instead, astronomers estimate mass by measuring how its gravity moves the surrounding material: stars, gas and dust orbiting the center of a galaxy. For quasars like TON 618 and OJ 287, the glow of the accretion disk and the motion of that hot infalling gas reveal the central mass. Each figure on this list is therefore an estimate with real uncertainty, refined over many observations.
Why Size Matters
Such enormous masses are hard to explain with ordinary growth. Astronomers believe ultramassive black holes form through repeated galaxy mergers, where two supermassive holes eventually merge, or through phases of extremely rapid accretion in the early universe. Studying them helps answer how galaxies and their central black holes co-evolve, and it sets the outer limits of black hole physics itself.
Fun Facts
- Phoenix A's ~100 billion solar masses is roughly 25,000 times the mass of the Milky Way's central black hole.
- TON 618 is one of the brightest quasars known, visible across billions of light-years.
- OJ 287 is a blazar with a smaller companion black hole orbiting its central giant.
- Every object on this list is at the center of a galaxy, mostly giant ellipticals in dense clusters.
- All 15 entries exceed 17 billion solar masses, thousands of times heavier than a typical supermassive black hole.
- Black holes on this scale are sometimes called ultramassive, above the usual supermassive class.
- NGC 1600 and OJ 287, the two lowest entries, are still larger than any black hole in our local group of galaxies.
- Masses on this list are indirect estimates, so future measurements can shift the precise numbers and order.
