Astronomers using the James Webb Space Telescope have identified three actively feeding supermassive black holes crowded inside a single galaxy from the universe's early adolescence, the first time such a system has been confirmed at that cosmic distance.
The galaxy, catalogued as J0148-4214, is seen as it appeared roughly 1.2 billion years after the Big Bang, its light having traveled more than 12.5 billion years to reach Webb's instruments. A team led by Hannah Übler of the Max Planck Institute for Extraterrestrial Physics, working with co-authors Giovanni Mazzolari and Roberto Maiolino, describes the discovery in a paper titled "BlackTHUNDER," published in Astronomy & Astrophysics on August 12.
A peculiar signal, unpacked
The team did not set out to find a triple system. Übler has said that light emerging from the galaxy's center had an oddly asymmetric shape in Webb's spectroscopic data, a clue that prompted closer analysis. Splitting the signal apart revealed two distinct broad-line regions — telltale signatures of gas swirling near a black hole — separated by only about 190 parsecs, or roughly 620 light-years. A third, fainter signature turned up far out in the galaxy's periphery, some 5,500 light-years from the center.
Using standard mass-estimation techniques, the researchers calculated the black holes at roughly 80 million, 2 million, and 600,000 times the mass of the sun. The two central black holes are close enough that models of dynamical friction suggest they could merge within a few hundred million years, a blink of an eye on cosmic timescales.
The smaller, off-center black hole is the more puzzling of the three. The team notes it appears to be accreting matter faster than current theoretical limits generally allow, and its origin is unresolved: it may have arrived through a separate galaxy merger, or it could be debris flung outward from an earlier three-body interaction among black holes near the galaxy's core. Outside researchers, including astrophysicist Julie Comerford, have pointed to both explanations as plausible without yet favoring one.
The result adds to a growing body of Webb observations suggesting that merging black holes, not just merging galaxies, may have played a bigger role in building up supermassive black hole mass in the early universe than previously modeled. As with most single-galaxy discoveries at these distances, the interpretation relies on spectroscopic inference rather than direct imaging of individual black holes, and confirmation will likely require additional observations of similar systems.
