A Glimpse of the Early Universe
A galaxy more than 12.5 billion light-years away has revealed a surprise: it hosts not one, not two, but three actively feeding supermassive black holes. The discovery, made possible by the James Webb Space Telescope (JWST), offers a rare view of how black holes grew and interacted when the universe was still in its infancy.
Light from the galaxy, catalogued as J0148-4214, has been traveling toward Earth for over 12.5 billion years. Because of the universe's expansion, this light is stretched to longer wavelengths, giving the galaxy a redshift of z=5.02. That places its observation at a time when the cosmos was only about 1.2 billion years old.
"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 (MPE) and lead author of the study, as reported by SciTechDaily. The findings appeared in the journal Astronomy & Astrophysics under the project name 'BlackTHUNDER'.
Locating the Invisible
Black holes themselves emit no light, but the material they pull in heats up and glows brightly. The research team, led by MPE scientists, identified three distinct regions where gas was moving at extreme speeds around the black holes, creating "broad-line" emissions in hydrogen, particularly the H-alpha feature.
The astronomers used JWST's Near-Infrared Spectrograph (NIRSpec) in its integral-field spectroscopy mode, a technique that maps how light varies across a galaxy. This was crucial because the black holes are too close together to be seen as separate points of light. Instead, the team employed a method called spectro-astrometry, which allowed them to pinpoint the black holes' locations with precision, as described by SciTechDaily.
Two of the black holes sit near the galaxy's center, separated by just 620 light-years in projection. The third lies about 5,500 light-years from the center. Their masses are estimated at roughly 80 million, 0.6 million, and 2 million times the mass of the Sun. All three are actively accreting matter, drawing gas from surrounding accretion disks.
A Dynamic Neighborhood
The presence of three black holes so close together in an ancient galaxy raises intriguing questions about how such systems evolve. The two central black holes, separated by only 620 light-years, are expected to merge within a few hundred million years, according to estimates reported by multiple sources. The Times of India suggests the merger could occur in less than 700 million years.
"It suggests that processes in the early Universe were efficient at bringing massive black holes together, setting the stage for the massive black hole mergers we expect to detect with future gravitational wave observatories," Übler said, as quoted by SciTechDaily.
The third black hole, located in the galaxy's outskirts, could have been kicked outward by the gravitational recoil of a previous merger, or it may be moving inward on a trajectory that could eventually bring it closer to the central pair, some reports speculate.
The galaxy's stellar mass is estimated at about 1.3 billion solar masses, based on JWST data, as reported by SciTechDaily. The smaller of the two central black holes is accreting matter at a rate that exceeds the Eddington limit, the theoretical maximum rate at which a black hole can swallow material while the outward pressure of radiation balances the inward pull of gravity. This suggests an extremely active feeding episode.
A Bridge to the Modern Universe
These observations align with the broader picture emerging from JWST studies of "little red dots," compact and extremely distant objects seen when the universe was about 1 billion years old. A separate paper, coauthored by researchers including Yiyang Zhang from Wuhan University and published in Nature Astronomy, analyzed over 200 such objects in the COSMOS-Web region.
That analysis suggests that in many little red dots, the central black hole contributes about 90% of the light, while the host galaxy provides only 10%. The host galaxies themselves are tiny — about 40% the size of typical galaxies at that epoch, or just 4% the size of the Milky Way, containing around 1 billion stars. This implies that supermassive black holes may gather most of their mass before the galaxy forms its stars.
The discovery of three active black holes in J0148-4214 is a striking example of how these early supermassive black holes might have grown so rapidly. Future gravitational wave observatories may one day detect the mergers that would result from systems like this one, offering a direct test of how such black holes formed and evolved in the early universe.