Webb measured a 13-billion-year-old black hole — it formed before its galaxy

The black hole in galaxy Abell2744-QSO1 has a mass of 50 million suns. Its host galaxy contains the rest. That ratio is wrong by every model we have: in any galaxy astronomers can reach today, the central black hole accounts for a fraction of a percent of the total stellar mass. Here, the black hole is two-thirds of everything.

That imbalance has a specific explanation, and it upends how astronomers have thought about the co-evolution of galaxies and their black holes. The team measured the galaxy’s metallicity — the concentration of elements heavier than hydrogen and helium, which stars manufacture during their lives — and found it at less than half a percent of the Sun’s. That near-zero reading means very few stars had lived and died in this galaxy when the Webb observations captured it. The black hole was already enormous in what was essentially a pristine, barely-born galaxy.

The finding is the result of a technique Webb makes possible for the first time. By mapping the motion and composition of gas orbiting close to the black hole — a dance of heated plasma drawn inward at measurable speeds — the team led by Roberto Maiolino at the University of Cambridge was able to calculate the black hole’s mass directly, without relying on theoretical proxies. It is the first direct mass measurement of any black hole from within the first billion years of the universe’s existence.

The standard picture in cosmology holds that galaxies and their central black holes grow together over billions of years, each feeding the other through mergers, gas inflows, and stellar feedback cycles. Abell2744-QSO1 breaks that picture. The galaxy is too pristine and too small relative to its black hole for the two to have evolved in lockstep. Something seeded this black hole early — possibly the direct collapse of a massive primordial gas cloud, or a black hole born from the first generation of enormous stars — and the galaxy grew around it afterward.

The result is not definitive. One object at extreme distance, measured under extreme observational conditions, is not enough to rewrite galaxy formation theory outright. The Cambridge team notes the measurement depends on assumptions about the geometry of the gas disk surrounding the black hole, and the Webb observations cannot fully resolve the smallest scales near the event horizon. Independent confirmation requires additional objects at similar distances.

Those objects are coming. Webb’s ongoing surveys of the early universe, particularly through programs targeting known galaxy overdensities like the Abell2744 cluster, will provide the sample. Maiolino’s team is already analyzing additional candidates from the same field. The first direct census of black hole masses in the first billion years after the Big Bang is now underway.

Tags: astronomy