Three Supermassive Black Holes Discovered in a Single Ancient Galaxy

The team used channel maps of the asymmetric central Hα profile to isolate two spatially distinct broad-line regions (BLRs) in the galactic center, separated by 190±40 parsecs (about 620 light-years). A third BLR was found in the galaxy's outskirts at a projected separation of 1.7 kiloparsecs (roughly 5,500 light-years) .

The Three Black Holes: Masses and Locations

Using single-epoch virial relations, the astronomers estimated the masses of the three black holes:

• Primary central black hole: log(M☉) = 7.9 ± 0.4, or approximately 80 million solar masses
• Secondary central black hole: log(M☉) = 5.8 ± 0.5, or roughly 600,000 solar masses
• Outer black hole: log(M☉) = 6.3 ± 0.4, or about 2 million solar masses

The study authors emphasize that these mass estimates carry substantial uncertainties—the core result is the discovery of three active massive black holes, not the precise mass values .

Two of the black holes lie close together in the galactic center, separated by only 620 light-years in projection. The third black hole is located in the galaxy's outer region, about 5,500 light-years from the center .

Early Universe Growth and the Black Hole Merger Path

J0148-4214 offers a unique window into how supermassive black holes grew so quickly in the early universe. The system suggests that mergers and interactions were efficient at bringing massive black holes together, providing a fast route for their rapid growth . This is the first evidence that triple black hole systems existed within the first 1.2 billion years of cosmic history.

The two central black holes, only 620 light-years apart, are expected to eventually merge. This close pair sets the stage for the massive black hole mergers that future gravitational wave observatories—such as the Laser Interferometer Space Antenna (LISA)—are designed to detect. The discovery demonstrates that such close pairs existed much earlier than previously known .

"This is the first evidence of three active black holes in a single galaxy in the distant universe," said Hannah Übler, research group leader at the Max Planck Institute for Extraterrestrial Physics and lead author of the study .

What This Means for Gravitational Wave Astronomy

The two central black holes in J0148-4214 are separated by just a few hundred parsecs, meaning they are gravitationally bound and on a collision course. When they eventually merge, they will produce gravitational waves detectable by space-based observatories like LISA, which is designed to observe mergers of massive black holes. The discovery shows that such close pairs existed much earlier in cosmic history than previously known, giving gravitational wave astronomers a clear target and confirming that the early universe was a bustling environment for black hole mergers .

Why This Discovery Matters

• A first of its kind: No galaxy in the early universe has ever been confirmed to host three actively accreting supermassive black holes.
• Rapid growth: The system suggests that galaxy mergers and interactions were efficient at bringing black holes together, explaining how they could grow so quickly after the Big Bang.
• Gravitational wave precursor: The close central pair is a probable future black hole merger, providing a natural laboratory for studying the events LISA will detect.
• JWST's unique capability: This detection was only possible because of JWST's spatially resolved spectroscopy, which can tease apart multiple active nuclei in distant, faint galaxies .

The findings are published in a preprint on arXiv.org under the study name "BlackTHUNDER: evidence for three massive black holes in a z~5 galaxy" .

What Comes Next

Astronomers plan to follow up with additional JWST observations to study the dynamics of the system in more detail and search for similar triple black hole galaxies in other early-universe fields. The discovery opens a new chapter in understanding how the most massive objects in the universe came to be—and how they continue to shape the cosmos through mergers.